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 $191.62   12.107%   $214.8194   $214.82   $214.80   $214.80  
  Purchase #2 $131.93   8.874%   $143.6375   $143.64   $143.65   $143.60  
  Purchase #3 $51.49   3.359%   $53.2195   $53.22   $53.20   $53.20  
  Purchase #4 $132.96   11.797%   $148.6453   $148.65   $148.65   $148.60  
  Purchase #5 $172.49   13.387%   $195.5812   $195.58   $195.60   $195.60  
  Purchase #6 $147.61   6.647%   $157.4216   $157.42   $157.40   $157.40  
  Purchase #7 $141.35   7.377%   $151.7774   $151.78   $151.80   $151.80  
  7 purchase totals = $969.45       $1,065.1019   $1,065.11   $1,065.10   $1,065.00