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 $98.33   13.115%   $111.226   $111.23   $111.25   $111.20  
  Purchase #2 $122.97   9.352%   $134.4702   $134.47   $134.45   $134.50  
  Purchase #3 $68.73   13.394%   $77.9357   $77.94   $77.95   $77.90  
  Purchase #4 $149.39   13.671%   $169.8131   $169.81   $169.80   $169.80  
  Purchase #5 $122.59   11.744%   $136.987   $136.99   $137.00   $137.00  
  Purchase #6 $225.39   8.277%   $244.0455   $244.05   $244.05   $244.00  
  Purchase #7 $170.34   4.747%   $178.426   $178.43   $178.45   $178.40  
  7 purchase totals = $957.74       $1,052.9035   $1,052.92   $1,052.95   $1,052.80