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 $86.99   8.322%   $94.2293   $94.23   $94.25   $94.20  
  Purchase #2 $208.41   6.700%   $222.3735   $222.37   $222.35   $222.40  
  Purchase #3 $158.47   7.447%   $170.2713   $170.27   $170.25   $170.30  
  Purchase #4 $148.34   12.593%   $167.0205   $167.02   $167.00   $167.00  
  Purchase #5 $136.84   10.799%   $151.6174   $151.62   $151.60   $151.60  
  Purchase #6 $79.67   11.397%   $88.75   $88.75   $88.75   $88.80  
  Purchase #7 $226.57   9.149%   $247.2989   $247.30   $247.30   $247.30  
  7 purchase totals = $1,045.29       $1,141.5609   $1,141.56   $1,141.50   $1,141.60