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 $180.44   8.290%   $195.3985   $195.40   $195.40   $195.40  
  Purchase #2 $205.32   6.776%   $219.2325   $219.23   $219.25   $219.20  
  Purchase #3 $240.77   7.566%   $258.9867   $258.99   $259.00   $259.00  
  Purchase #4 $22.49   11.614%   $25.102   $25.10   $25.10   $25.10  
  Purchase #5 $60.67   6.230%   $64.4497   $64.45   $64.45   $64.40  
  Purchase #6 $129.72   5.790%   $137.2308   $137.23   $137.25   $137.20  
  Purchase #7 $116.73   8.714%   $126.9019   $126.90   $126.90   $126.90  
  7 purchase totals = $956.14       $1,027.3021   $1,027.30   $1,027.35   $1,027.20