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 $238.63   12.873%   $269.3488   $269.35   $269.35   $269.30  
  Purchase #2 $163.99   7.351%   $176.0449   $176.04   $176.05   $176.00  
  Purchase #3 $50.49   8.385%   $54.7236   $54.72   $54.70   $54.70  
  Purchase #4 $233.98   13.525%   $265.6258   $265.63   $265.65   $265.60  
  Purchase #5 $193.29   13.478%   $219.3416   $219.34   $219.35   $219.30  
  Purchase #6 $138.72   3.430%   $143.4781   $143.48   $143.50   $143.50  
  Purchase #7 $223.32   10.514%   $246.7999   $246.80   $246.80   $246.80  
  7 purchase totals = $1,242.42       $1,375.3627   $1,375.36   $1,375.40   $1,375.20