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 $167.96   8.128%   $181.6118   $181.61   $181.60   $181.60  
  Purchase #2 $248.39   6.252%   $263.9193   $263.92   $263.90   $263.90  
  Purchase #3 $119.30   13.540%   $135.4532   $135.45   $135.45   $135.50  
  Purchase #4 $66.74   9.470%   $73.0603   $73.06   $73.05   $73.10  
  Purchase #5 $19.42   11.347%   $21.6236   $21.62   $21.60   $21.60  
  Purchase #6 $99.79   7.145%   $106.92   $106.92   $106.90   $106.90  
  Purchase #7 $50.33   5.287%   $52.9909   $52.99   $53.00   $53.00  
  7 purchase totals = $771.93       $835.5791   $835.57   $835.50   $835.60