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 $32.82   6.410%   $34.9238   $34.92   $34.90   $34.90  
  Purchase #2 $184.92   5.217%   $194.5673   $194.57   $194.55   $194.60  
  Purchase #3 $206.80   5.764%   $218.72   $218.72   $218.70   $218.70  
  Purchase #4 $73.68   9.677%   $80.81   $80.81   $80.80   $80.80  
  Purchase #5 $168.85   10.606%   $186.7582   $186.76   $186.75   $186.80  
  Purchase #6 $144.49   10.623%   $159.8392   $159.84   $159.85   $159.80  
  Purchase #7 $8.96   11.581%   $9.9977   $10.00   $10.00   $10.00  
  7 purchase totals = $820.52       $885.6162   $885.62   $885.55   $885.60