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 $76.95   9.853%   $84.5319   $84.53   $84.55   $84.50  
  Purchase #2 $169.54   11.678%   $189.3389   $189.34   $189.35   $189.30  
  Purchase #3 $237.88   6.551%   $253.4635   $253.46   $253.45   $253.50  
  Purchase #4 $55.46   6.315%   $58.9623   $58.96   $58.95   $59.00  
  Purchase #5 $110.90   11.873%   $124.0672   $124.07   $124.05   $124.10  
  Purchase #6 $136.92   12.841%   $154.5019   $154.50   $154.50   $154.50  
  Purchase #7 $184.57   11.390%   $205.5925   $205.59   $205.60   $205.60  
  7 purchase totals = $972.22       $1,070.4582   $1,070.45   $1,070.45   $1,070.50