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 $82.98   12.130%   $93.0455   $93.05   $93.05   $93.00  
  Purchase #2 $248.91   10.837%   $275.8844   $275.88   $275.90   $275.90  
  Purchase #3 $19.77   7.291%   $21.2114   $21.21   $21.20   $21.20  
  Purchase #4 $203.69   9.673%   $223.3929   $223.39   $223.40   $223.40  
  Purchase #5 $152.90   8.203%   $165.4424   $165.44   $165.45   $165.40  
  Purchase #6 $11.48   7.551%   $12.3469   $12.35   $12.35   $12.30  
  Purchase #7 $247.39   12.795%   $279.0436   $279.04   $279.05   $279.00  
  7 purchase totals = $967.12       $1,070.3671   $1,070.36   $1,070.40   $1,070.20