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 $224.42   5.491%   $236.7429   $236.74   $236.75   $236.70  
  Purchase #2 $168.96   13.607%   $191.9504   $191.95   $191.95   $192.00  
  Purchase #3 $207.75   11.107%   $230.8248   $230.82   $230.80   $230.80  
  Purchase #4 $129.35   11.178%   $143.8087   $143.81   $143.80   $143.80  
  Purchase #5 $98.40   4.871%   $103.1931   $103.19   $103.20   $103.20  
  Purchase #6 $103.68   6.718%   $110.6452   $110.65   $110.65   $110.60  
  Purchase #7 $235.65   10.196%   $259.6769   $259.68   $259.70   $259.70  
  7 purchase totals = $1,168.21       $1,276.8420   $1,276.84   $1,276.85   $1,276.80