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 $246.68   11.828%   $275.8573   $275.86   $275.85   $275.90  
  Purchase #2 $205.61   7.239%   $220.4941   $220.49   $220.50   $220.50  
  Purchase #3 $69.41   13.479%   $78.7658   $78.77   $78.75   $78.80  
  Purchase #4 $142.83   5.424%   $150.5771   $150.58   $150.60   $150.60  
  Purchase #5 $247.62   9.142%   $270.2574   $270.26   $270.25   $270.30  
  Purchase #6 $112.87   10.169%   $124.3478   $124.35   $124.35   $124.30  
  Purchase #7 $118.78   11.319%   $132.2247   $132.22   $132.20   $132.20  
  7 purchase totals = $1,143.80       $1,252.5242   $1,252.53   $1,252.50   $1,252.60