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 $214.41   5.769%   $226.7793   $226.78   $226.80   $226.80  
  Purchase #2 $238.73   11.707%   $266.6781   $266.68   $266.70   $266.70  
  Purchase #3 $17.82   3.679%   $18.4756   $18.48   $18.50   $18.50  
  Purchase #4 $131.75   10.836%   $146.0264   $146.03   $146.05   $146.00  
  Purchase #5 $33.75   7.166%   $36.1685   $36.17   $36.15   $36.20  
  Purchase #6 $203.79   10.818%   $225.836   $225.84   $225.85   $225.80  
  Purchase #7 $80.29   10.215%   $88.4916   $88.49   $88.50   $88.50  
  7 purchase totals = $920.54       $1,008.4555   $1,008.47   $1,008.55   $1,008.50