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 $250.65   6.332%   $266.5212   $266.52   $266.50   $266.50  
  Purchase #2 $101.48   10.415%   $112.0491   $112.05   $112.05   $112.00  
  Purchase #3 $104.47   6.131%   $110.8751   $110.88   $110.90   $110.90  
  Purchase #4 $150.97   6.498%   $160.78   $160.78   $160.80   $160.80  
  Purchase #5 $58.44   5.367%   $61.5765   $61.58   $61.60   $61.60  
  Purchase #6 $120.86   12.490%   $135.9554   $135.96   $135.95   $136.00  
  Purchase #7 $214.58   13.155%   $242.808   $242.81   $242.80   $242.80  
  7 purchase totals = $1,001.45       $1,090.5653   $1,090.58   $1,090.60   $1,090.60