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 $180.46   4.129%   $187.9112   $187.91   $187.90   $187.90  
  Purchase #2 $62.26   10.764%   $68.9617   $68.96   $68.95   $69.00  
  Purchase #3 $241.44   6.355%   $256.7835   $256.78   $256.80   $256.80  
  Purchase #4 $150.77   10.140%   $166.0581   $166.06   $166.05   $166.10  
  Purchase #5 $200.29   12.637%   $225.6006   $225.60   $225.60   $225.60  
  Purchase #6 $87.36   10.807%   $96.801   $96.80   $96.80   $96.80  
  Purchase #7 $28.52   5.776%   $30.1673   $30.17   $30.15   $30.20  
  7 purchase totals = $951.10       $1,032.2834   $1,032.28   $1,032.25   $1,032.40