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 $237.27   6.164%   $251.8953   $251.90   $251.90   $251.90  
  Purchase #2 $12.59   11.651%   $14.0569   $14.06   $14.05   $14.10  
  Purchase #3 $122.65   4.733%   $128.455   $128.46   $128.45   $128.50  
  Purchase #4 $162.38   5.319%   $171.017   $171.02   $171.00   $171.00  
  Purchase #5 $232.89   10.338%   $256.9662   $256.97   $256.95   $257.00  
  Purchase #6 $187.63   13.740%   $213.4104   $213.41   $213.40   $213.40  
  Purchase #7 $184.36   9.115%   $201.1644   $201.16   $201.15   $201.20  
  7 purchase totals = $1,139.77       $1,236.9652   $1,236.98   $1,236.90   $1,237.10