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 $74.62   13.734%   $84.8683   $84.87   $84.85   $84.90  
  Purchase #2 $139.28   8.668%   $151.3528   $151.35   $151.35   $151.40  
  Purchase #3 $61.88   6.733%   $66.0464   $66.05   $66.05   $66.00  
  Purchase #4 $80.74   13.782%   $91.8676   $91.87   $91.85   $91.90  
  Purchase #5 $96.31   11.175%   $107.0726   $107.07   $107.05   $107.10  
  Purchase #6 $225.39   6.171%   $239.2988   $239.30   $239.30   $239.30  
  Purchase #7 $75.68   11.277%   $84.2144   $84.21   $84.20   $84.20  
  7 purchase totals = $753.90       $824.7209   $824.72   $824.65   $824.80