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 $88.34   11.764%   $98.7323   $98.73   $98.75   $98.70  
  Purchase #2 $202.89   4.362%   $211.7401   $211.74   $211.75   $211.70  
  Purchase #3 $219.38   3.716%   $227.5322   $227.53   $227.55   $227.50  
  Purchase #4 $114.79   9.871%   $126.1209   $126.12   $126.10   $126.10  
  Purchase #5 $8.99   7.253%   $9.642   $9.64   $9.65   $9.60  
  Purchase #6 $205.47   3.164%   $211.9711   $211.97   $211.95   $212.00  
  Purchase #7 $222.37   5.572%   $234.7605   $234.76   $234.75   $234.80  
  7 purchase totals = $1,062.23       $1,120.4991   $1,120.49   $1,120.50   $1,120.40