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 $230.76   6.174%   $245.0071   $245.01   $245.00   $245.00  
  Purchase #2 $17.29   6.180%   $18.3585   $18.36   $18.35   $18.40  
  Purchase #3 $36.99   12.459%   $41.5986   $41.60   $41.60   $41.60  
  Purchase #4 $242.67   6.405%   $258.213   $258.21   $258.20   $258.20  
  Purchase #5 $154.34   12.376%   $173.4411   $173.44   $173.45   $173.40  
  Purchase #6 $56.36   10.653%   $62.364   $62.36   $62.35   $62.40  
  Purchase #7 $199.88   10.302%   $220.4716   $220.47   $220.45   $220.50  
  7 purchase totals = $938.29       $1,019.4539   $1,019.45   $1,019.40   $1,019.50