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 $83.47   10.790%   $92.4764   $92.48   $92.50   $92.50  
  Purchase #2 $187.28   12.840%   $211.3268   $211.33   $211.35   $211.30  
  Purchase #3 $10.75   8.598%   $11.6743   $11.67   $11.65   $11.70  
  Purchase #4 $96.39   8.175%   $104.2699   $104.27   $104.25   $104.30  
  Purchase #5 $41.26   7.353%   $44.2938   $44.29   $44.30   $44.30  
  Purchase #6 $153.79   12.271%   $172.6616   $172.66   $172.65   $172.70  
  Purchase #7 $162.25   7.640%   $174.6459   $174.65   $174.65   $174.60  
  7 purchase totals = $735.19       $811.3487   $811.35   $811.35   $811.40