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 $56.52   8.260%   $61.1886   $61.19   $61.20   $61.20  
  Purchase #2 $9.52   11.730%   $10.6367   $10.64   $10.65   $10.60  
  Purchase #3 $71.76   4.494%   $74.9849   $74.98   $75.00   $75.00  
  Purchase #4 $6.99   13.534%   $7.936   $7.94   $7.95   $7.90  
  Purchase #5 $16.43   11.103%   $18.2542   $18.25   $18.25   $18.30  
  Purchase #6 $75.49   12.619%   $85.0161   $85.02   $85.00   $85.00  
  Purchase #7 $109.73   7.825%   $118.3164   $118.32   $118.30   $118.30  
  7 purchase totals = $346.44       $376.3329   $376.34   $376.35   $376.30