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 $32.90   4.731%   $34.4565   $34.46   $34.45   $34.50  
  Purchase #2 $39.97   11.781%   $44.6789   $44.68   $44.70   $44.70  
  Purchase #3 $204.73   13.854%   $233.0933   $233.09   $233.10   $233.10  
  Purchase #4 $211.58   7.146%   $226.6995   $226.70   $226.70   $226.70  
  Purchase #5 $86.56   12.293%   $97.2008   $97.20   $97.20   $97.20  
  Purchase #6 $215.65   11.661%   $240.7969   $240.80   $240.80   $240.80  
  Purchase #7 $164.93   3.684%   $171.006   $171.01   $171.00   $171.00  
  7 purchase totals = $956.32       $1,047.9319   $1,047.94   $1,047.95   $1,048.00