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 $173.25   13.622%   $196.8501   $196.85   $196.85   $196.90  
  Purchase #2 $225.86   11.840%   $252.6018   $252.60   $252.60   $252.60  
  Purchase #3 $136.29   11.313%   $151.7085   $151.71   $151.70   $151.70  
  Purchase #4 $30.60   3.112%   $31.5523   $31.55   $31.55   $31.60  
  Purchase #5 $244.80   12.330%   $274.9838   $274.98   $275.00   $275.00  
  Purchase #6 $128.48   5.216%   $135.1815   $135.18   $135.20   $135.20  
  Purchase #7 $235.50   10.411%   $260.0179   $260.02   $260.00   $260.00  
  7 purchase totals = $1,174.78       $1,302.8959   $1,302.89   $1,302.90   $1,303.00