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 $214.73   8.106%   $232.136   $232.14   $232.15   $232.10  
  Purchase #2 $15.60   8.286%   $16.8926   $16.89   $16.90   $16.90  
  Purchase #3 $49.81   4.494%   $52.0485   $52.05   $52.05   $52.00  
  Purchase #4 $193.61   4.292%   $201.9197   $201.92   $201.90   $201.90  
  Purchase #5 $198.51   7.229%   $212.8603   $212.86   $212.85   $212.90  
  Purchase #6 $26.33   12.702%   $29.6744   $29.67   $29.65   $29.70  
  Purchase #7 $20.66   9.667%   $22.6572   $22.66   $22.65   $22.70  
  7 purchase totals = $719.25       $768.1887   $768.19   $768.15   $768.20