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 $186.36   10.122%   $205.2234   $205.22   $205.20   $205.20  
  Purchase #2 $74.77   9.622%   $81.9644   $81.96   $81.95   $82.00  
  Purchase #3 $68.99   6.718%   $73.6247   $73.62   $73.60   $73.60  
  Purchase #4 $94.29   7.286%   $101.16   $101.16   $101.15   $101.20  
  Purchase #5 $174.57   5.562%   $184.2796   $184.28   $184.30   $184.30  
  Purchase #6 $127.83   12.511%   $143.8228   $143.82   $143.80   $143.80  
  Purchase #7 $57.30   12.731%   $64.5949   $64.59   $64.60   $64.60  
  7 purchase totals = $784.11       $854.6698   $854.65   $854.60   $854.70