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 $222.62   8.595%   $241.7542   $241.75   $241.75   $241.80  
  Purchase #2 $58.95   9.627%   $64.6251   $64.63   $64.65   $64.60  
  Purchase #3 $106.41   4.510%   $111.2091   $111.21   $111.20   $111.20  
  Purchase #4 $214.70   6.215%   $228.0436   $228.04   $228.05   $228.00  
  Purchase #5 $245.83   13.703%   $279.5161   $279.52   $279.50   $279.50  
  Purchase #6 $150.30   10.245%   $165.6982   $165.70   $165.70   $165.70  
  Purchase #7 $164.47   10.307%   $181.4219   $181.42   $181.40   $181.40  
  7 purchase totals = $1,163.28       $1,272.2682   $1,272.27   $1,272.25   $1,272.20