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 $245.41   3.174%   $253.1993   $253.20   $253.20   $253.20  
  Purchase #2 $128.33   13.509%   $145.6661   $145.67   $145.65   $145.70  
  Purchase #3 $198.32   9.807%   $217.7692   $217.77   $217.75   $217.80  
  Purchase #4 $36.83   7.212%   $39.4862   $39.49   $39.50   $39.50  
  Purchase #5 $234.85   7.870%   $253.3327   $253.33   $253.35   $253.30  
  Purchase #6 $49.30   10.845%   $54.6466   $54.65   $54.65   $54.60  
  Purchase #7 $64.58   9.514%   $70.7241   $70.72   $70.70   $70.70  
  7 purchase totals = $957.62       $1,034.8242   $1,034.83   $1,034.80   $1,034.80