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 $197.87   7.532%   $212.7736   $212.77   $212.75   $212.80  
  Purchase #2 $126.64   6.849%   $135.3136   $135.31   $135.30   $135.30  
  Purchase #3 $45.64   8.462%   $49.5021   $49.50   $49.50   $49.50  
  Purchase #4 $200.93   5.470%   $211.9209   $211.92   $211.90   $211.90  
  Purchase #5 $109.51   5.273%   $115.2845   $115.28   $115.30   $115.30  
  Purchase #6 $234.58   10.769%   $259.8419   $259.84   $259.85   $259.80  
  Purchase #7 $51.46   7.352%   $55.2433   $55.24   $55.25   $55.20  
  7 purchase totals = $966.63       $1,039.8799   $1,039.86   $1,039.85   $1,039.80