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 $96.98   13.453%   $110.0267   $110.03   $110.05   $110.00  
  Purchase #2 $15.52   9.813%   $17.043   $17.04   $17.05   $17.00  
  Purchase #3 $106.78   5.123%   $112.2503   $112.25   $112.25   $112.30  
  Purchase #4 $245.63   10.648%   $271.7847   $271.78   $271.80   $271.80  
  Purchase #5 $60.53   10.176%   $66.6895   $66.69   $66.70   $66.70  
  Purchase #6 $230.30   7.578%   $247.7521   $247.75   $247.75   $247.80  
  Purchase #7 $186.58   12.852%   $210.5593   $210.56   $210.55   $210.60  
  7 purchase totals = $942.32       $1,036.1056   $1,036.10   $1,036.15   $1,036.20