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 $32.29   12.362%   $36.2817   $36.28   $36.30   $36.30  
  Purchase #2 $244.39   8.292%   $264.6548   $264.65   $264.65   $264.70  
  Purchase #3 $119.94   9.768%   $131.6557   $131.66   $131.65   $131.70  
  Purchase #4 $82.72   3.701%   $85.7815   $85.78   $85.80   $85.80  
  Purchase #5 $23.40   6.265%   $24.866   $24.87   $24.85   $24.90  
  Purchase #6 $237.28   3.525%   $245.6441   $245.64   $245.65   $245.60  
  Purchase #7 $80.44   13.564%   $91.3509   $91.35   $91.35   $91.40  
  7 purchase totals = $820.46       $880.2347   $880.23   $880.25   $880.40