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 $84.99   9.580%   $93.132   $93.13   $93.15   $93.10  
  Purchase #2 $233.55   6.780%   $249.3847   $249.38   $249.40   $249.40  
  Purchase #3 $240.66   11.699%   $268.8148   $268.81   $268.80   $268.80  
  Purchase #4 $195.47   8.609%   $212.298   $212.30   $212.30   $212.30  
  Purchase #5 $196.52   10.355%   $216.8696   $216.87   $216.85   $216.90  
  Purchase #6 $88.48   3.142%   $91.26   $91.26   $91.25   $91.30  
  Purchase #7 $122.41   7.445%   $131.5234   $131.52   $131.50   $131.50  
  7 purchase totals = $1,162.08       $1,263.2825   $1,263.27   $1,263.25   $1,263.30