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 $243.98   9.828%   $267.9584   $267.96   $267.95   $268.00  
  Purchase #2 $73.58   5.176%   $77.3885   $77.39   $77.40   $77.40  
  Purchase #3 $70.93   10.371%   $78.2862   $78.29   $78.30   $78.30  
  Purchase #4 $191.30   10.710%   $211.7882   $211.79   $211.80   $211.80  
  Purchase #5 $221.33   10.332%   $244.1978   $244.20   $244.20   $244.20  
  Purchase #6 $34.86   4.799%   $36.5329   $36.53   $36.55   $36.50  
  Purchase #7 $162.29   3.859%   $168.5528   $168.55   $168.55   $168.60  
  7 purchase totals = $998.27       $1,084.7048   $1,084.71   $1,084.75   $1,084.80