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 $85.97   9.839%   $94.4286   $94.43   $94.45   $94.40  
  Purchase #2 $59.37   10.677%   $65.7089   $65.71   $65.70   $65.70  
  Purchase #3 $36.39   13.421%   $41.2739   $41.27   $41.25   $41.30  
  Purchase #4 $203.28   9.369%   $222.3253   $222.33   $222.35   $222.30  
  Purchase #5 $218.64   4.629%   $228.7608   $228.76   $228.75   $228.80  
  Purchase #6 $230.49   8.153%   $249.2818   $249.28   $249.30   $249.30  
  Purchase #7 $164.47   10.311%   $181.4285   $181.43   $181.45   $181.40  
  7 purchase totals = $998.61       $1,083.2078   $1,083.21   $1,083.25   $1,083.20