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 $70.25   7.198%   $75.3066   $75.31   $75.30   $75.30  
  Purchase #2 $16.98   7.818%   $18.3075   $18.31   $18.30   $18.30  
  Purchase #3 $14.46   12.271%   $16.2344   $16.23   $16.25   $16.20  
  Purchase #4 $101.42   7.619%   $109.1472   $109.15   $109.15   $109.10  
  Purchase #5 $142.62   12.226%   $160.0567   $160.06   $160.05   $160.10  
  Purchase #6 $184.52   3.481%   $190.9431   $190.94   $190.95   $190.90  
  Purchase #7 $113.84   4.772%   $119.2724   $119.27   $119.25   $119.30  
  7 purchase totals = $644.09       $689.2679   $689.27   $689.25   $689.20