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 $53.57   12.484%   $60.2577   $60.26   $60.25   $60.30  
  Purchase #2 $232.87   12.593%   $262.1953   $262.20   $262.20   $262.20  
  Purchase #3 $48.65   6.268%   $51.6994   $51.70   $51.70   $51.70  
  Purchase #4 $151.39   12.819%   $170.7967   $170.80   $170.80   $170.80  
  Purchase #5 $16.25   9.225%   $17.7491   $17.75   $17.75   $17.70  
  Purchase #6 $40.44   11.167%   $44.9559   $44.96   $44.95   $45.00  
  Purchase #7 $196.37   3.476%   $203.1958   $203.20   $203.20   $203.20  
  7 purchase totals = $739.54       $810.8499   $810.87   $810.85   $810.90