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 $88.62   4.548%   $92.6504   $92.65   $92.65   $92.70  
  Purchase #2 $111.61   11.854%   $124.8402   $124.84   $124.85   $124.80  
  Purchase #3 $119.62   9.623%   $131.131   $131.13   $131.15   $131.10  
  Purchase #4 $75.31   8.765%   $81.9109   $81.91   $81.90   $81.90  
  Purchase #5 $45.59   12.461%   $51.271   $51.27   $51.25   $51.30  
  Purchase #6 $240.39   7.496%   $258.4096   $258.41   $258.40   $258.40  
  Purchase #7 $223.50   12.776%   $252.0544   $252.05   $252.05   $252.10  
  7 purchase totals = $904.64       $992.2675   $992.26   $992.25   $992.30