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 $240.78   11.107%   $267.5234   $267.52   $267.50   $267.50  
  Purchase #2 $113.31   6.130%   $120.2559   $120.26   $120.25   $120.30  
  Purchase #3 $224.83   3.478%   $232.6496   $232.65   $232.65   $232.60  
  Purchase #4 $111.50   12.644%   $125.5981   $125.60   $125.60   $125.60  
  Purchase #5 $196.77   11.205%   $218.8181   $218.82   $218.80   $218.80  
  Purchase #6 $180.56   5.339%   $190.2001   $190.20   $190.20   $190.20  
  Purchase #7 $110.38   8.317%   $119.5603   $119.56   $119.55   $119.60  
  7 purchase totals = $1,178.13       $1,274.6055   $1,274.61   $1,274.55   $1,274.60