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 $141.86   12.625%   $159.7698   $159.77   $159.75   $159.80  
  Purchase #2 $201.99   9.789%   $221.7628   $221.76   $221.75   $221.80  
  Purchase #3 $72.84   12.626%   $82.0368   $82.04   $82.05   $82.00  
  Purchase #4 $99.71   8.574%   $108.2591   $108.26   $108.25   $108.30  
  Purchase #5 $106.44   4.119%   $110.8243   $110.82   $110.80   $110.80  
  Purchase #6 $208.31   6.147%   $221.1148   $221.11   $221.10   $221.10  
  Purchase #7 $119.57   8.570%   $129.8171   $129.82   $129.80   $129.80  
  7 purchase totals = $950.72       $1,033.5847   $1,033.58   $1,033.50   $1,033.60