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 $249.61   7.454%   $268.2159   $268.22   $268.20   $268.20  
  Purchase #2 $62.49   4.510%   $65.3083   $65.31   $65.30   $65.30  
  Purchase #3 $243.97   10.442%   $269.4453   $269.45   $269.45   $269.40  
  Purchase #4 $188.84   11.613%   $210.77   $210.77   $210.75   $210.80  
  Purchase #5 $131.77   3.834%   $136.8221   $136.82   $136.80   $136.80  
  Purchase #6 $51.72   13.689%   $58.8   $58.80   $58.80   $58.80  
  Purchase #7 $60.78   3.578%   $62.9547   $62.95   $62.95   $63.00  
  7 purchase totals = $989.18       $1,072.3163   $1,072.32   $1,072.25   $1,072.30