Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $187.37   3.727%   $194.3533   $194.35   $194.35   $194.40  
  Purchase #2 $138.96   4.814%   $145.6495   $145.65   $145.65   $145.60  
  Purchase #3 $241.71   11.297%   $269.016   $269.02   $269.00   $269.00  
  Purchase #4 $157.63   8.191%   $170.5415   $170.54   $170.55   $170.50  
  Purchase #5 $200.58   9.293%   $219.2199   $219.22   $219.20   $219.20  
  Purchase #6 $203.64   13.777%   $231.6955   $231.70   $231.70   $231.70  
  Purchase #7 $105.78   7.811%   $114.0425   $114.04   $114.05   $114.00  
  7 purchase totals = $1,235.67       $1,344.5182   $1,344.52   $1,344.50   $1,344.40