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 $26.47   4.461%   $27.6508   $27.65   $27.65   $27.70  
  Purchase #2 $52.87   7.333%   $56.747   $56.75   $56.75   $56.70  
  Purchase #3 $94.84   10.580%   $104.8741   $104.87   $104.85   $104.90  
  Purchase #4 $59.79   3.616%   $61.952   $61.95   $61.95   $62.00  
  Purchase #5 $78.36   6.666%   $83.5835   $83.58   $83.60   $83.60  
  Purchase #6 $202.61   13.511%   $229.9846   $229.98   $230.00   $230.00  
  Purchase #7 $138.74   6.815%   $148.1951   $148.20   $148.20   $148.20  
  7 purchase totals = $653.68       $712.9871   $712.98   $713.00   $713.10