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 $207.27   12.662%   $233.5145   $233.51   $233.50   $233.50  
  Purchase #2 $97.52   6.337%   $103.6998   $103.70   $103.70   $103.70  
  Purchase #3 $157.29   11.690%   $175.6772   $175.68   $175.70   $175.70  
  Purchase #4 $5.56   5.640%   $5.8736   $5.87   $5.85   $5.90  
  Purchase #5 $40.79   13.676%   $46.3684   $46.37   $46.35   $46.40  
  Purchase #6 $122.69   5.467%   $129.3975   $129.40   $129.40   $129.40  
  Purchase #7 $75.79   3.821%   $78.6859   $78.69   $78.70   $78.70  
  7 purchase totals = $706.91       $773.2169   $773.22   $773.20   $773.30