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 $82.91   5.556%   $87.5165   $87.52   $87.50   $87.50  
  Purchase #2 $215.56   7.448%   $231.6149   $231.61   $231.60   $231.60  
  Purchase #3 $104.39   12.586%   $117.5285   $117.53   $117.55   $117.50  
  Purchase #4 $234.97   12.438%   $264.1956   $264.20   $264.20   $264.20  
  Purchase #5 $20.29   13.328%   $22.9943   $22.99   $23.00   $23.00  
  Purchase #6 $88.89   5.819%   $94.0625   $94.06   $94.05   $94.10  
  Purchase #7 $30.39   12.287%   $34.124   $34.12   $34.10   $34.10  
  7 purchase totals = $777.40       $852.0363   $852.03   $852.00   $852.00