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 $201.87   6.164%   $214.3133   $214.31   $214.30   $214.30  
  Purchase #2 $87.61   6.464%   $93.2731   $93.27   $93.25   $93.30  
  Purchase #3 $239.84   13.371%   $271.909   $271.91   $271.90   $271.90  
  Purchase #4 $75.88   9.264%   $82.9095   $82.91   $82.90   $82.90  
  Purchase #5 $9.83   5.201%   $10.3413   $10.34   $10.35   $10.30  
  Purchase #6 $116.67   3.729%   $121.0206   $121.02   $121.00   $121.00  
  Purchase #7 $231.33   5.284%   $243.5535   $243.55   $243.55   $243.60  
  7 purchase totals = $963.03       $1,037.3203   $1,037.31   $1,037.25   $1,037.30