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 $6.40   5.250%   $6.736   $6.74   $6.75   $6.70  
  Purchase #2 $126.45   12.283%   $141.9819   $141.98   $142.00   $142.00  
  Purchase #3 $110.39   7.156%   $118.2895   $118.29   $118.30   $118.30  
  Purchase #4 $61.75   6.662%   $65.8638   $65.86   $65.85   $65.90  
  Purchase #5 $138.83   9.613%   $152.1757   $152.18   $152.20   $152.20  
  Purchase #6 $44.48   6.363%   $47.3103   $47.31   $47.30   $47.30  
  Purchase #7 $79.78   3.164%   $82.3042   $82.30   $82.30   $82.30  
  7 purchase totals = $568.08       $614.6614   $614.66   $614.70   $614.70