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 $228.80   6.744%   $244.2303   $244.23   $244.25   $244.20  
  Purchase #2 $149.88   10.701%   $165.9187   $165.92   $165.90   $165.90  
  Purchase #3 $193.58   3.225%   $199.823   $199.82   $199.80   $199.80  
  Purchase #4 $114.41   7.711%   $123.2322   $123.23   $123.25   $123.20  
  Purchase #5 $126.45   7.551%   $135.9982   $136.00   $136.00   $136.00  
  Purchase #6 $209.39   11.117%   $232.6679   $232.67   $232.65   $232.70  
  Purchase #7 $144.92   5.167%   $152.408   $152.41   $152.40   $152.40  
  7 purchase totals = $1,167.43       $1,254.2783   $1,254.28   $1,254.25   $1,254.20