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 $114.46   12.228%   $128.4562   $128.46   $128.45   $128.50  
  Purchase #2 $138.68   8.107%   $149.9228   $149.92   $149.90   $149.90  
  Purchase #3 $105.48   8.269%   $114.2021   $114.20   $114.20   $114.20  
  Purchase #4 $160.37   9.132%   $175.015   $175.02   $175.00   $175.00  
  Purchase #5 $81.33   6.787%   $86.8499   $86.85   $86.85   $86.80  
  Purchase #6 $181.76   8.777%   $197.7131   $197.71   $197.70   $197.70  
  Purchase #7 $111.54   7.482%   $119.8854   $119.89   $119.90   $119.90  
  7 purchase totals = $893.62       $972.0445   $972.05   $972.00   $972.00