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 $224.83   7.430%   $241.5349   $241.53   $241.55   $241.50  
  Purchase #2 $132.91   9.257%   $145.2135   $145.21   $145.20   $145.20  
  Purchase #3 $69.77   8.837%   $75.9356   $75.94   $75.95   $75.90  
  Purchase #4 $208.86   9.827%   $229.3847   $229.38   $229.40   $229.40  
  Purchase #5 $51.84   9.286%   $56.6539   $56.65   $56.65   $56.70  
  Purchase #6 $112.78   6.806%   $120.4558   $120.46   $120.45   $120.50  
  Purchase #7 $190.28   9.528%   $208.4099   $208.41   $208.40   $208.40  
  7 purchase totals = $991.27       $1,077.5883   $1,077.58   $1,077.60   $1,077.60