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 $60.62   10.707%   $67.1106   $67.11   $67.10   $67.10  
  Purchase #2 $243.45   13.506%   $276.3304   $276.33   $276.35   $276.30  
  Purchase #3 $21.38   4.815%   $22.4094   $22.41   $22.40   $22.40  
  Purchase #4 $225.63   9.643%   $247.3875   $247.39   $247.40   $247.40  
  Purchase #5 $81.99   3.657%   $84.9884   $84.99   $85.00   $85.00  
  Purchase #6 $79.59   12.347%   $89.417   $89.42   $89.40   $89.40  
  Purchase #7 $79.45   10.646%   $87.9082   $87.91   $87.90   $87.90  
  7 purchase totals = $792.11       $875.5515   $875.56   $875.55   $875.50