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 $157.33   8.181%   $170.2012   $170.20   $170.20   $170.20  
  Purchase #2 $245.81   12.332%   $276.1233   $276.12   $276.10   $276.10  
  Purchase #3 $63.97   3.549%   $66.2403   $66.24   $66.25   $66.20  
  Purchase #4 $244.89   10.205%   $269.881   $269.88   $269.90   $269.90  
  Purchase #5 $115.29   3.592%   $119.4312   $119.43   $119.45   $119.40  
  Purchase #6 $184.58   11.764%   $206.294   $206.29   $206.30   $206.30  
  Purchase #7 $80.67   5.221%   $84.8818   $84.88   $84.90   $84.90  
  7 purchase totals = $1,092.54       $1,193.0528   $1,193.04   $1,193.10   $1,193.00