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 $158.46   5.854%   $167.7362   $167.74   $167.75   $167.70  
  Purchase #2 $208.83   12.122%   $234.1444   $234.14   $234.15   $234.10  
  Purchase #3 $170.83   13.426%   $193.7656   $193.77   $193.75   $193.80  
  Purchase #4 $90.36   5.689%   $95.5006   $95.50   $95.50   $95.50  
  Purchase #5 $176.51   7.265%   $189.3335   $189.33   $189.35   $189.30  
  Purchase #6 $101.96   5.274%   $107.3374   $107.34   $107.35   $107.30  
  Purchase #7 $112.28   9.662%   $123.1285   $123.13   $123.15   $123.10  
  7 purchase totals = $1,019.23       $1,110.9462   $1,110.95   $1,111.00   $1,110.80