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 $206.53   12.653%   $232.6622   $232.66   $232.65   $232.70  
  Purchase #2 $134.98   13.206%   $152.8055   $152.81   $152.80   $152.80  
  Purchase #3 $204.49   3.643%   $211.9396   $211.94   $211.95   $211.90  
  Purchase #4 $123.54   10.588%   $136.6204   $136.62   $136.60   $136.60  
  Purchase #5 $148.65   7.761%   $160.1867   $160.19   $160.20   $160.20  
  Purchase #6 $62.83   10.368%   $69.3442   $69.34   $69.35   $69.30  
  Purchase #7 $62.76   6.760%   $67.0026   $67.00   $67.00   $67.00  
  7 purchase totals = $943.78       $1,030.5612   $1,030.56   $1,030.55   $1,030.50