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 $33.77   8.457%   $36.6259   $36.63   $36.65   $36.60  
  Purchase #2 $194.43   13.650%   $220.9697   $220.97   $220.95   $221.00  
  Purchase #3 $199.31   12.382%   $223.9886   $223.99   $224.00   $224.00  
  Purchase #4 $249.29   5.102%   $262.0088   $262.01   $262.00   $262.00  
  Purchase #5 $31.88   4.795%   $33.4086   $33.41   $33.40   $33.40  
  Purchase #6 $200.61   12.215%   $225.1145   $225.11   $225.10   $225.10  
  Purchase #7 $169.50   4.750%   $177.5513   $177.55   $177.55   $177.60  
  7 purchase totals = $1,078.79       $1,179.6674   $1,179.67   $1,179.65   $1,179.70