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 $59.89   13.314%   $67.8638   $67.86   $67.85   $67.90  
  Purchase #2 $177.82   7.111%   $190.4648   $190.46   $190.45   $190.50  
  Purchase #3 $159.98   8.331%   $173.3079   $173.31   $173.30   $173.30  
  Purchase #4 $166.92   8.224%   $180.6475   $180.65   $180.65   $180.60  
  Purchase #5 $126.33   7.401%   $135.6797   $135.68   $135.70   $135.70  
  Purchase #6 $237.29   4.351%   $247.6145   $247.61   $247.60   $247.60  
  Purchase #7 $45.74   6.214%   $48.5823   $48.58   $48.60   $48.60  
  7 purchase totals = $973.97       $1,044.1605   $1,044.15   $1,044.15   $1,044.20