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 $41.39   7.104%   $44.3303   $44.33   $44.35   $44.30  
  Purchase #2 $75.38   12.363%   $84.6992   $84.70   $84.70   $84.70  
  Purchase #3 $238.93   3.405%   $247.0656   $247.07   $247.05   $247.10  
  Purchase #4 $157.87   5.871%   $167.1385   $167.14   $167.15   $167.10  
  Purchase #5 $98.43   10.219%   $108.4886   $108.49   $108.50   $108.50  
  Purchase #6 $99.43   6.862%   $106.2529   $106.25   $106.25   $106.30  
  Purchase #7 $180.90   12.767%   $203.9955   $204.00   $204.00   $204.00  
  7 purchase totals = $892.33       $961.9706   $961.98   $962.00   $962.00