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 $61.71   8.508%   $66.9603   $66.96   $66.95   $67.00  
  Purchase #2 $168.40   12.631%   $189.6706   $189.67   $189.65   $189.70  
  Purchase #3 $22.64   6.737%   $24.1653   $24.17   $24.15   $24.20  
  Purchase #4 $69.57   7.823%   $75.0125   $75.01   $75.00   $75.00  
  Purchase #5 $141.33   3.563%   $146.3656   $146.37   $146.35   $146.40  
  Purchase #6 $209.46   6.124%   $222.2873   $222.29   $222.30   $222.30  
  Purchase #7 $62.30   8.811%   $67.7893   $67.79   $67.80   $67.80  
  7 purchase totals = $735.41       $792.2509   $792.26   $792.20   $792.40