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 $86.92   8.381%   $94.2048   $94.20   $94.20   $94.20  
  Purchase #2 $201.41   13.578%   $228.7574   $228.76   $228.75   $228.80  
  Purchase #3 $90.98   12.703%   $102.5372   $102.54   $102.55   $102.50  
  Purchase #4 $166.76   9.295%   $182.2603   $182.26   $182.25   $182.30  
  Purchase #5 $140.83   9.714%   $154.5102   $154.51   $154.50   $154.50  
  Purchase #6 $106.40   11.756%   $118.9084   $118.91   $118.90   $118.90  
  Purchase #7 $118.80   10.277%   $131.0091   $131.01   $131.00   $131.00  
  7 purchase totals = $912.10       $1,012.1874   $1,012.19   $1,012.15   $1,012.20