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 $234.84   11.428%   $261.6775   $261.68   $261.70   $261.70  
  Purchase #2 $72.74   3.122%   $75.0109   $75.01   $75.00   $75.00  
  Purchase #3 $13.49   3.745%   $13.9952   $14.00   $14.00   $14.00  
  Purchase #4 $94.84   12.264%   $106.4712   $106.47   $106.45   $106.50  
  Purchase #5 $219.89   7.113%   $235.5308   $235.53   $235.55   $235.50  
  Purchase #6 $61.68   10.461%   $68.1323   $68.13   $68.15   $68.10  
  Purchase #7 $92.99   5.338%   $97.9538   $97.95   $97.95   $98.00  
  7 purchase totals = $790.47       $858.7717   $858.77   $858.80   $858.80