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 $86.43   12.654%   $97.3669   $97.37   $97.35   $97.40  
  Purchase #2 $58.41   11.133%   $64.9128   $64.91   $64.90   $64.90  
  Purchase #3 $68.39   9.445%   $74.8494   $74.85   $74.85   $74.80  
  Purchase #4 $181.87   13.780%   $206.9317   $206.93   $206.95   $206.90  
  Purchase #5 $127.34   3.314%   $131.56   $131.56   $131.55   $131.60  
  Purchase #6 $157.31   8.678%   $170.9614   $170.96   $170.95   $171.00  
  Purchase #7 $106.54   8.471%   $115.565   $115.57   $115.55   $115.60  
  7 purchase totals = $786.29       $862.1472   $862.15   $862.10   $862.20