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 $48.41   4.680%   $50.6756   $50.68   $50.70   $50.70  
  Purchase #2 $70.26   3.739%   $72.887   $72.89   $72.90   $72.90  
  Purchase #3 $97.61   4.819%   $102.3138   $102.31   $102.30   $102.30  
  Purchase #4 $104.79   8.724%   $113.9319   $113.93   $113.95   $113.90  
  Purchase #5 $239.75   3.281%   $247.6162   $247.62   $247.60   $247.60  
  Purchase #6 $241.39   9.171%   $263.5279   $263.53   $263.55   $263.50  
  Purchase #7 $224.83   7.761%   $242.2791   $242.28   $242.30   $242.30  
  7 purchase totals = $1,027.04       $1,093.2315   $1,093.24   $1,093.30   $1,093.20