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 $46.67   13.503%   $52.9719   $52.97   $52.95   $53.00  
  Purchase #2 $45.37   8.561%   $49.2541   $49.25   $49.25   $49.30  
  Purchase #3 $122.95   3.459%   $127.2028   $127.20   $127.20   $127.20  
  Purchase #4 $244.34   7.323%   $262.233   $262.23   $262.25   $262.20  
  Purchase #5 $100.91   10.185%   $111.1877   $111.19   $111.20   $111.20  
  Purchase #6 $211.71   9.738%   $232.3263   $232.33   $232.35   $232.30  
  Purchase #7 $175.57   7.744%   $189.1661   $189.17   $189.15   $189.20  
  7 purchase totals = $947.52       $1,024.3419   $1,024.34   $1,024.35   $1,024.40