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 $95.72   9.638%   $104.9455   $104.95   $104.95   $104.90  
  Purchase #2 $230.86   11.150%   $256.6009   $256.60   $256.60   $256.60  
  Purchase #3 $36.68   7.334%   $39.3701   $39.37   $39.35   $39.40  
  Purchase #4 $247.73   12.742%   $279.2958   $279.30   $279.30   $279.30  
  Purchase #5 $8.26   9.455%   $9.041   $9.04   $9.05   $9.00  
  Purchase #6 $40.53   3.296%   $41.8659   $41.87   $41.85   $41.90  
  Purchase #7 $63.27   8.755%   $68.8093   $68.81   $68.80   $68.80  
  7 purchase totals = $723.05       $799.9285   $799.94   $799.90   $799.90