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 $101.41   10.713%   $112.2741   $112.27   $112.25   $112.30  
  Purchase #2 $137.51   6.754%   $146.7974   $146.80   $146.80   $146.80  
  Purchase #3 $34.85   5.580%   $36.7946   $36.79   $36.80   $36.80  
  Purchase #4 $60.56   7.216%   $64.93   $64.93   $64.95   $64.90  
  Purchase #5 $201.66   8.110%   $218.0146   $218.01   $218.00   $218.00  
  Purchase #6 $145.75   6.762%   $155.6056   $155.61   $155.60   $155.60  
  Purchase #7 $165.76   5.324%   $174.5851   $174.59   $174.60   $174.60  
  7 purchase totals = $847.50       $909.0014   $909.00   $909.00   $909.00