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 $54.86   12.172%   $61.5376   $61.54   $61.55   $61.50  
  Purchase #2 $219.41   11.140%   $243.8523   $243.85   $243.85   $243.90  
  Purchase #3 $222.57   12.434%   $250.2444   $250.24   $250.25   $250.20  
  Purchase #4 $74.43   6.299%   $79.1183   $79.12   $79.10   $79.10  
  Purchase #5 $110.48   10.519%   $122.1014   $122.10   $122.10   $122.10  
  Purchase #6 $232.54   5.550%   $245.446   $245.45   $245.45   $245.40  
  Purchase #7 $86.82   4.531%   $90.7538   $90.75   $90.75   $90.80  
  7 purchase totals = $1,001.11       $1,093.0538   $1,093.05   $1,093.05   $1,093.00