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 $232.31   13.580%   $263.8577   $263.86   $263.85   $263.90  
  Purchase #2 $52.85   13.389%   $59.9261   $59.93   $59.95   $59.90  
  Purchase #3 $182.77   13.147%   $206.7988   $206.80   $206.80   $206.80  
  Purchase #4 $95.43   9.698%   $104.6848   $104.68   $104.70   $104.70  
  Purchase #5 $245.88   9.385%   $268.9558   $268.96   $268.95   $269.00  
  Purchase #6 $85.65   12.258%   $96.149   $96.15   $96.15   $96.10  
  Purchase #7 $71.88   6.245%   $76.3689   $76.37   $76.35   $76.40  
  7 purchase totals = $966.77       $1,076.7411   $1,076.75   $1,076.75   $1,076.80