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 $244.52   4.490%   $255.4989   $255.50   $255.50   $255.50  
  Purchase #2 $156.45   7.349%   $167.9475   $167.95   $167.95   $167.90  
  Purchase #3 $165.47   7.827%   $178.4213   $178.42   $178.40   $178.40  
  Purchase #4 $34.29   6.611%   $36.5569   $36.56   $36.55   $36.60  
  Purchase #5 $242.49   3.146%   $250.1187   $250.12   $250.10   $250.10  
  Purchase #6 $86.37   12.453%   $97.1257   $97.13   $97.15   $97.10  
  Purchase #7 $53.60   9.310%   $58.5902   $58.59   $58.60   $58.60  
  7 purchase totals = $983.19       $1,044.2592   $1,044.27   $1,044.25   $1,044.20