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 $224.78   13.303%   $254.6825   $254.68   $254.70   $254.70  
  Purchase #2 $113.90   4.653%   $119.1998   $119.20   $119.20   $119.20  
  Purchase #3 $138.89   6.476%   $147.8845   $147.88   $147.90   $147.90  
  Purchase #4 $106.31   10.618%   $117.598   $117.60   $117.60   $117.60  
  Purchase #5 $201.32   12.712%   $226.9118   $226.91   $226.90   $226.90  
  Purchase #6 $104.36   11.146%   $115.992   $115.99   $116.00   $116.00  
  Purchase #7 $205.33   8.251%   $222.2718   $222.27   $222.25   $222.30  
  7 purchase totals = $1,094.89       $1,204.5404   $1,204.53   $1,204.55   $1,204.60