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 $110.77   10.160%   $122.0242   $122.02   $122.00   $122.00  
  Purchase #2 $227.45   4.185%   $236.9688   $236.97   $236.95   $237.00  
  Purchase #3 $202.61   10.653%   $224.194   $224.19   $224.20   $224.20  
  Purchase #4 $162.74   12.261%   $182.6936   $182.69   $182.70   $182.70  
  Purchase #5 $114.73   9.344%   $125.4504   $125.45   $125.45   $125.50  
  Purchase #6 $237.49   6.690%   $253.3781   $253.38   $253.40   $253.40  
  Purchase #7 $188.46   6.310%   $200.3518   $200.35   $200.35   $200.40  
  7 purchase totals = $1,244.25       $1,345.0609   $1,345.05   $1,345.05   $1,345.20