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 $233.49   8.700%   $253.8036   $253.80   $253.80   $253.80  
  Purchase #2 $100.89   7.245%   $108.1995   $108.20   $108.20   $108.20  
  Purchase #3 $55.95   10.783%   $61.9831   $61.98   $62.00   $62.00  
  Purchase #4 $177.69   7.544%   $191.0949   $191.09   $191.10   $191.10  
  Purchase #5 $238.59   6.274%   $253.5591   $253.56   $253.55   $253.60  
  Purchase #6 $136.48   6.204%   $144.9472   $144.95   $144.95   $144.90  
  Purchase #7 $235.36   5.347%   $247.9447   $247.94   $247.95   $247.90  
  7 purchase totals = $1,178.45       $1,261.5321   $1,261.52   $1,261.55   $1,261.50