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 $182.98   6.461%   $194.8023   $194.80   $194.80   $194.80  
  Purchase #2 $182.69   11.137%   $203.0362   $203.04   $203.05   $203.00  
  Purchase #3 $103.46   12.239%   $116.1225   $116.12   $116.10   $116.10  
  Purchase #4 $22.31   10.499%   $24.6523   $24.65   $24.65   $24.70  
  Purchase #5 $247.74   13.322%   $280.7439   $280.74   $280.75   $280.70  
  Purchase #6 $248.59   5.862%   $263.1623   $263.16   $263.15   $263.20  
  Purchase #7 $126.69   4.731%   $132.6837   $132.68   $132.70   $132.70  
  7 purchase totals = $1,114.46       $1,215.2032   $1,215.19   $1,215.20   $1,215.20