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 $229.42   6.809%   $245.0412   $245.04   $245.05   $245.00  
  Purchase #2 $165.28   3.802%   $171.5639   $171.56   $171.55   $171.60  
  Purchase #3 $155.71   12.322%   $174.8966   $174.90   $174.90   $174.90  
  Purchase #4 $93.72   8.421%   $101.6122   $101.61   $101.60   $101.60  
  Purchase #5 $20.59   9.583%   $22.5631   $22.56   $22.55   $22.60  
  Purchase #6 $164.75   7.281%   $176.7454   $176.75   $176.75   $176.70  
  Purchase #7 $158.99   5.241%   $167.3227   $167.32   $167.30   $167.30  
  7 purchase totals = $988.46       $1,059.7451   $1,059.74   $1,059.70   $1,059.70