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 $219.52   11.567%   $244.9119   $244.91   $244.90   $244.90  
  Purchase #2 $245.37   8.525%   $266.2878   $266.29   $266.30   $266.30  
  Purchase #3 $124.76   7.372%   $133.9573   $133.96   $133.95   $134.00  
  Purchase #4 $84.38   6.144%   $89.5643   $89.56   $89.55   $89.60  
  Purchase #5 $155.78   13.843%   $177.3446   $177.34   $177.35   $177.30  
  Purchase #6 $128.77   3.688%   $133.519   $133.52   $133.50   $133.50  
  Purchase #7 $40.74   5.776%   $43.0931   $43.09   $43.10   $43.10  
  7 purchase totals = $999.32       $1,088.6780   $1,088.67   $1,088.65   $1,088.70