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 $237.27   11.695%   $265.0187   $265.02   $265.00   $265.00  
  Purchase #2 $6.59   10.223%   $7.2637   $7.26   $7.25   $7.30  
  Purchase #3 $160.88   10.848%   $178.3323   $178.33   $178.35   $178.30  
  Purchase #4 $160.84   6.857%   $171.8688   $171.87   $171.85   $171.90  
  Purchase #5 $166.71   11.788%   $186.3618   $186.36   $186.35   $186.40  
  Purchase #6 $235.57   6.806%   $251.6029   $251.60   $251.60   $251.60  
  Purchase #7 $28.83   10.375%   $31.8211   $31.82   $31.80   $31.80  
  7 purchase totals = $996.69       $1,092.2693   $1,092.26   $1,092.20   $1,092.30