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 $217.50   11.140%   $241.7295   $241.73   $241.75   $241.70  
  Purchase #2 $58.53   10.349%   $64.5873   $64.59   $64.60   $64.60  
  Purchase #3 $108.47   4.442%   $113.2882   $113.29   $113.30   $113.30  
  Purchase #4 $145.53   7.613%   $156.6092   $156.61   $156.60   $156.60  
  Purchase #5 $77.37   4.461%   $80.8215   $80.82   $80.80   $80.80  
  Purchase #6 $204.50   3.742%   $212.1524   $212.15   $212.15   $212.20  
  Purchase #7 $109.39   9.205%   $119.4593   $119.46   $119.45   $119.50  
  7 purchase totals = $921.29       $988.6474   $988.65   $988.65   $988.70