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 $214.27   12.704%   $241.4909   $241.49   $241.50   $241.50  
  Purchase #2 $113.42   4.651%   $118.6952   $118.70   $118.70   $118.70  
  Purchase #3 $137.86   8.111%   $149.0418   $149.04   $149.05   $149.00  
  Purchase #4 $88.54   8.830%   $96.3581   $96.36   $96.35   $96.40  
  Purchase #5 $184.89   5.433%   $194.9351   $194.94   $194.95   $194.90  
  Purchase #6 $226.29   11.507%   $252.3292   $252.33   $252.35   $252.30  
  Purchase #7 $13.79   13.393%   $15.6369   $15.64   $15.65   $15.60  
  7 purchase totals = $979.06       $1,068.4872   $1,068.50   $1,068.55   $1,068.40