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 $41.81   13.172%   $47.3172   $47.32   $47.30   $47.30  
  Purchase #2 $101.53   9.479%   $111.154   $111.15   $111.15   $111.20  
  Purchase #3 $61.66   13.562%   $70.0223   $70.02   $70.00   $70.00  
  Purchase #4 $165.57   7.722%   $178.3553   $178.36   $178.35   $178.40  
  Purchase #5 $188.98   4.635%   $197.7392   $197.74   $197.75   $197.70  
  Purchase #6 $178.57   5.180%   $187.8199   $187.82   $187.80   $187.80  
  Purchase #7 $119.61   9.160%   $130.5663   $130.57   $130.55   $130.60  
  7 purchase totals = $857.73       $922.9742   $922.98   $922.90   $923.00