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 $109.95   7.692%   $118.4074   $118.41   $118.40   $118.40  
  Purchase #2 $41.75   6.755%   $44.5702   $44.57   $44.55   $44.60  
  Purchase #3 $156.56   4.805%   $164.0827   $164.08   $164.10   $164.10  
  Purchase #4 $247.36   4.206%   $257.764   $257.76   $257.75   $257.80  
  Purchase #5 $205.28   9.119%   $223.9995   $224.00   $224.00   $224.00  
  Purchase #6 $220.53   6.736%   $235.3849   $235.38   $235.40   $235.40  
  Purchase #7 $5.70   6.578%   $6.0749   $6.07   $6.05   $6.10  
  7 purchase totals = $987.13       $1,050.2836   $1,050.27   $1,050.25   $1,050.40