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 $24.59   9.586%   $26.9472   $26.95   $26.95   $26.90  
  Purchase #2 $56.29   10.659%   $62.29   $62.29   $62.30   $62.30  
  Purchase #3 $29.81   5.192%   $31.3577   $31.36   $31.35   $31.40  
  Purchase #4 $203.40   6.640%   $216.9058   $216.91   $216.90   $216.90  
  Purchase #5 $138.48   7.207%   $148.4603   $148.46   $148.45   $148.50  
  Purchase #6 $59.35   4.232%   $61.8617   $61.86   $61.85   $61.90  
  Purchase #7 $25.70   8.873%   $27.9804   $27.98   $28.00   $28.00  
  7 purchase totals = $537.62       $575.8031   $575.81   $575.80   $575.90