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 $41.77   6.648%   $44.5469   $44.55   $44.55   $44.50  
  Purchase #2 $113.28   11.810%   $126.6584   $126.66   $126.65   $126.70  
  Purchase #3 $92.93   7.174%   $99.5968   $99.60   $99.60   $99.60  
  Purchase #4 $181.57   6.594%   $193.5427   $193.54   $193.55   $193.50  
  Purchase #5 $59.70   5.311%   $62.8707   $62.87   $62.85   $62.90  
  Purchase #6 $170.42   3.816%   $176.9232   $176.92   $176.90   $176.90  
  Purchase #7 $202.63   11.850%   $226.6417   $226.64   $226.65   $226.60  
  7 purchase totals = $862.30       $930.7804   $930.78   $930.75   $930.70