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 $206.64   8.291%   $223.7725   $223.77   $223.75   $223.80  
  Purchase #2 $228.44   5.762%   $241.6027   $241.60   $241.60   $241.60  
  Purchase #3 $171.25   5.398%   $180.4941   $180.49   $180.50   $180.50  
  Purchase #4 $49.25   5.798%   $52.1055   $52.11   $52.10   $52.10  
  Purchase #5 $92.74   11.781%   $103.6657   $103.67   $103.65   $103.70  
  Purchase #6 $90.84   11.635%   $101.4092   $101.41   $101.40   $101.40  
  Purchase #7 $36.87   5.681%   $38.9646   $38.96   $38.95   $39.00  
  7 purchase totals = $876.03       $942.0143   $942.01   $941.95   $942.10