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 $243.84   11.834%   $272.696   $272.70   $272.70   $272.70  
  Purchase #2 $56.83   5.379%   $59.8869   $59.89   $59.90   $59.90  
  Purchase #3 $144.62   7.179%   $155.0023   $155.00   $155.00   $155.00  
  Purchase #4 $168.59   9.121%   $183.9671   $183.97   $183.95   $184.00  
  Purchase #5 $150.58   5.817%   $159.3392   $159.34   $159.35   $159.30  
  Purchase #6 $240.93   6.668%   $256.9952   $257.00   $257.00   $257.00  
  Purchase #7 $249.64   5.419%   $263.168   $263.17   $263.15   $263.20  
  7 purchase totals = $1,255.03       $1,351.0547   $1,351.07   $1,351.05   $1,351.10