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 $97.95   8.414%   $106.1915   $106.19   $106.20   $106.20  
  Purchase #2 $62.38   7.148%   $66.8389   $66.84   $66.85   $66.80  
  Purchase #3 $231.83   6.397%   $246.6602   $246.66   $246.65   $246.70  
  Purchase #4 $186.96   5.247%   $196.7698   $196.77   $196.75   $196.80  
  Purchase #5 $188.79   7.696%   $203.3193   $203.32   $203.30   $203.30  
  Purchase #6 $148.25   13.455%   $168.197   $168.20   $168.20   $168.20  
  Purchase #7 $147.92   4.783%   $154.995   $155.00   $155.00   $155.00  
  7 purchase totals = $1,064.08       $1,142.9717   $1,142.98   $1,142.95   $1,143.00