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 $72.86   6.436%   $77.5493   $77.55   $77.55   $77.50  
  Purchase #2 $34.27   5.808%   $36.2604   $36.26   $36.25   $36.30  
  Purchase #3 $109.43   9.249%   $119.5512   $119.55   $119.55   $119.60  
  Purchase #4 $126.60   11.838%   $141.5869   $141.59   $141.60   $141.60  
  Purchase #5 $189.88   11.334%   $211.401   $211.40   $211.40   $211.40  
  Purchase #6 $147.78   12.766%   $166.6456   $166.65   $166.65   $166.60  
  Purchase #7 $154.46   12.222%   $173.3381   $173.34   $173.35   $173.30  
  7 purchase totals = $835.28       $926.3325   $926.34   $926.35   $926.30