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 $25.53   6.644%   $27.2262   $27.23   $27.25   $27.20  
  Purchase #2 $150.85   3.141%   $155.5882   $155.59   $155.60   $155.60  
  Purchase #3 $186.41   13.343%   $211.2827   $211.28   $211.30   $211.30  
  Purchase #4 $195.94   8.410%   $212.4186   $212.42   $212.40   $212.40  
  Purchase #5 $160.90   11.443%   $179.3118   $179.31   $179.30   $179.30  
  Purchase #6 $172.84   5.359%   $182.1025   $182.10   $182.10   $182.10  
  Purchase #7 $56.36   6.436%   $59.9873   $59.99   $60.00   $60.00  
  7 purchase totals = $948.83       $1,027.9173   $1,027.92   $1,027.95   $1,027.90