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 $160.82   12.399%   $180.7601   $180.76   $180.75   $180.80  
  Purchase #2 $186.40   13.709%   $211.9536   $211.95   $211.95   $212.00  
  Purchase #3 $98.41   5.343%   $103.668   $103.67   $103.65   $103.70  
  Purchase #4 $46.57   9.481%   $50.9853   $50.99   $51.00   $51.00  
  Purchase #5 $61.81   11.855%   $69.1376   $69.14   $69.15   $69.10  
  Purchase #6 $229.36   13.770%   $260.9429   $260.94   $260.95   $260.90  
  Purchase #7 $191.74   12.699%   $216.0891   $216.09   $216.10   $216.10  
  7 purchase totals = $975.11       $1,093.5366   $1,093.54   $1,093.55   $1,093.60