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 $236.53   6.514%   $251.9376   $251.94   $251.95   $251.90  
  Purchase #2 $79.93   13.227%   $90.5023   $90.50   $90.50   $90.50  
  Purchase #3 $195.68   3.212%   $201.9652   $201.97   $201.95   $202.00  
  Purchase #4 $94.53   11.669%   $105.5607   $105.56   $105.55   $105.60  
  Purchase #5 $156.79   11.406%   $174.6735   $174.67   $174.65   $174.70  
  Purchase #6 $225.53   8.114%   $243.8295   $243.83   $243.85   $243.80  
  Purchase #7 $79.95   6.425%   $85.0868   $85.09   $85.10   $85.10  
  7 purchase totals = $1,068.94       $1,153.5556   $1,153.56   $1,153.55   $1,153.60