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 $92.68   6.778%   $98.9619   $98.96   $98.95   $99.00  
  Purchase #2 $87.98   11.764%   $98.33   $98.33   $98.35   $98.30  
  Purchase #3 $78.77   7.425%   $84.6187   $84.62   $84.60   $84.60  
  Purchase #4 $249.56   3.150%   $257.4211   $257.42   $257.40   $257.40  
  Purchase #5 $240.86   11.729%   $269.1105   $269.11   $269.10   $269.10  
  Purchase #6 $222.51   6.643%   $237.2913   $237.29   $237.30   $237.30  
  Purchase #7 $189.97   6.504%   $202.3256   $202.33   $202.35   $202.30  
  7 purchase totals = $1,162.33       $1,248.0591   $1,248.06   $1,248.05   $1,248.00