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 $222.40   7.764%   $239.6671   $239.67   $239.65   $239.70  
  Purchase #2 $60.28   8.784%   $65.575   $65.58   $65.60   $65.60  
  Purchase #3 $178.49   10.531%   $197.2868   $197.29   $197.30   $197.30  
  Purchase #4 $159.31   7.551%   $171.3395   $171.34   $171.35   $171.30  
  Purchase #5 $67.86   10.666%   $75.0979   $75.10   $75.10   $75.10  
  Purchase #6 $250.96   13.262%   $284.2423   $284.24   $284.25   $284.20  
  Purchase #7 $24.84   4.600%   $25.9826   $25.98   $26.00   $26.00  
  7 purchase totals = $964.14       $1,059.1912   $1,059.20   $1,059.25   $1,059.20