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 $80.61   8.516%   $87.4747   $87.47   $87.45   $87.50  
  Purchase #2 $83.28   4.419%   $86.9601   $86.96   $86.95   $87.00  
  Purchase #3 $224.77   12.669%   $253.2461   $253.25   $253.25   $253.20  
  Purchase #4 $57.69   8.508%   $62.5983   $62.60   $62.60   $62.60  
  Purchase #5 $237.52   6.781%   $253.6262   $253.63   $253.65   $253.60  
  Purchase #6 $173.65   9.301%   $189.8012   $189.80   $189.80   $189.80  
  Purchase #7 $111.46   4.297%   $116.2494   $116.25   $116.25   $116.20  
  7 purchase totals = $968.98       $1,049.9560   $1,049.96   $1,049.95   $1,049.90