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 $173.92   6.511%   $185.2439   $185.24   $185.25   $185.20  
  Purchase #2 $145.44   3.112%   $149.9661   $149.97   $149.95   $150.00  
  Purchase #3 $84.92   10.540%   $93.8706   $93.87   $93.85   $93.90  
  Purchase #4 $7.28   10.772%   $8.0642   $8.06   $8.05   $8.10  
  Purchase #5 $99.71   13.428%   $113.0991   $113.10   $113.10   $113.10  
  Purchase #6 $91.97   9.443%   $100.6547   $100.65   $100.65   $100.70  
  Purchase #7 $223.76   6.344%   $237.9553   $237.96   $237.95   $238.00  
  7 purchase totals = $827.00       $888.8539   $888.85   $888.80   $889.00