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 $59.33   11.379%   $66.0812   $66.08   $66.10   $66.10  
  Purchase #2 $102.91   3.468%   $106.4789   $106.48   $106.50   $106.50  
  Purchase #3 $92.63   5.224%   $97.469   $97.47   $97.45   $97.50  
  Purchase #4 $55.40   6.578%   $59.0442   $59.04   $59.05   $59.00  
  Purchase #5 $235.76   13.516%   $267.6253   $267.63   $267.65   $267.60  
  Purchase #6 $39.90   3.283%   $41.2099   $41.21   $41.20   $41.20  
  Purchase #7 $229.26   9.508%   $251.058   $251.06   $251.05   $251.10  
  7 purchase totals = $815.19       $888.9665   $888.97   $889.00   $889.00