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 $178.41   8.246%   $193.1217   $193.12   $193.10   $193.10  
  Purchase #2 $222.88   7.639%   $239.9058   $239.91   $239.90   $239.90  
  Purchase #3 $107.96   9.460%   $118.173   $118.17   $118.15   $118.20  
  Purchase #4 $156.41   7.481%   $168.111   $168.11   $168.10   $168.10  
  Purchase #5 $127.60   8.545%   $138.5034   $138.50   $138.50   $138.50  
  Purchase #6 $40.26   3.494%   $41.6667   $41.67   $41.65   $41.70  
  Purchase #7 $68.87   10.404%   $76.0352   $76.04   $76.05   $76.00  
  7 purchase totals = $902.39       $975.5168   $975.52   $975.45   $975.50