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 $32.79   10.811%   $36.3349   $36.33   $36.35   $36.30  
  Purchase #2 $224.68   10.230%   $247.6648   $247.66   $247.65   $247.70  
  Purchase #3 $174.43   11.847%   $195.0947   $195.09   $195.10   $195.10  
  Purchase #4 $9.64   7.193%   $10.3334   $10.33   $10.35   $10.30  
  Purchase #5 $24.40   9.304%   $26.6702   $26.67   $26.65   $26.70  
  Purchase #6 $186.85   6.147%   $198.3357   $198.34   $198.35   $198.30  
  Purchase #7 $121.81   11.457%   $135.7658   $135.77   $135.75   $135.80  
  7 purchase totals = $774.60       $850.1995   $850.19   $850.20   $850.20