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 $194.43   6.210%   $206.5041   $206.50   $206.50   $206.50  
  Purchase #2 $28.65   5.131%   $30.12   $30.12   $30.10   $30.10  
  Purchase #3 $116.61   8.625%   $126.6676   $126.67   $126.65   $126.70  
  Purchase #4 $115.35   12.279%   $129.5138   $129.51   $129.50   $129.50  
  Purchase #5 $189.69   4.373%   $197.9851   $197.99   $198.00   $198.00  
  Purchase #6 $58.42   13.759%   $66.458   $66.46   $66.45   $66.50  
  Purchase #7 $244.97   12.701%   $276.0836   $276.08   $276.10   $276.10  
  7 purchase totals = $948.12       $1,033.3322   $1,033.33   $1,033.30   $1,033.40