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 $216.91   13.137%   $245.4055   $245.41   $245.40   $245.40  
  Purchase #2 $137.71   13.510%   $156.3146   $156.31   $156.30   $156.30  
  Purchase #3 $171.64   3.107%   $176.9729   $176.97   $176.95   $177.00  
  Purchase #4 $152.52   3.465%   $157.8048   $157.80   $157.80   $157.80  
  Purchase #5 $126.59   13.592%   $143.7961   $143.80   $143.80   $143.80  
  Purchase #6 $57.82   3.737%   $59.9807   $59.98   $60.00   $60.00  
  Purchase #7 $231.38   9.632%   $253.6665   $253.67   $253.65   $253.70  
  7 purchase totals = $1,094.57       $1,193.9411   $1,193.94   $1,193.90   $1,194.00