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 $150.49   12.638%   $169.5089   $169.51   $169.50   $169.50  
  Purchase #2 $223.28   13.583%   $253.6081   $253.61   $253.60   $253.60  
  Purchase #3 $171.97   12.150%   $192.8644   $192.86   $192.85   $192.90  
  Purchase #4 $230.58   13.273%   $261.1849   $261.18   $261.20   $261.20  
  Purchase #5 $23.72   9.528%   $25.98   $25.98   $26.00   $26.00  
  Purchase #6 $149.59   6.787%   $159.7427   $159.74   $159.75   $159.70  
  Purchase #7 $160.79   4.833%   $168.561   $168.56   $168.55   $168.60  
  7 purchase totals = $1,110.42       $1,231.4500   $1,231.44   $1,231.45   $1,231.50