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 $210.67   12.821%   $237.68   $237.68   $237.70   $237.70  
  Purchase #2 $45.89   13.336%   $52.0099   $52.01   $52.00   $52.00  
  Purchase #3 $23.55   7.527%   $25.3226   $25.32   $25.30   $25.30  
  Purchase #4 $62.36   6.849%   $66.631   $66.63   $66.65   $66.60  
  Purchase #5 $36.79   6.605%   $39.22   $39.22   $39.20   $39.20  
  Purchase #6 $229.82   9.313%   $251.2231   $251.22   $251.20   $251.20  
  Purchase #7 $183.56   8.805%   $199.7225   $199.72   $199.70   $199.70  
  7 purchase totals = $792.64       $871.8091   $871.80   $871.75   $871.70