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 $68.43   13.314%   $77.5408   $77.54   $77.55   $77.50  
  Purchase #2 $155.89   9.549%   $170.7759   $170.78   $170.80   $170.80  
  Purchase #3 $25.65   11.770%   $28.669   $28.67   $28.65   $28.70  
  Purchase #4 $229.62   3.266%   $237.1194   $237.12   $237.10   $237.10  
  Purchase #5 $51.43   11.572%   $57.3815   $57.38   $57.40   $57.40  
  Purchase #6 $242.27   7.612%   $260.7116   $260.71   $260.70   $260.70  
  Purchase #7 $207.82   9.765%   $228.1136   $228.11   $228.10   $228.10  
  7 purchase totals = $981.11       $1,060.3118   $1,060.31   $1,060.30   $1,060.30