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 $39.79   8.552%   $43.1928   $43.19   $43.20   $43.20  
  Purchase #2 $118.83   8.842%   $129.3369   $129.34   $129.35   $129.30  
  Purchase #3 $88.85   13.596%   $100.93   $100.93   $100.95   $100.90  
  Purchase #4 $242.89   8.136%   $262.6515   $262.65   $262.65   $262.70  
  Purchase #5 $43.51   11.693%   $48.5976   $48.60   $48.60   $48.60  
  Purchase #6 $223.96   13.565%   $254.3402   $254.34   $254.35   $254.30  
  Purchase #7 $197.86   8.368%   $214.4169   $214.42   $214.40   $214.40  
  7 purchase totals = $955.69       $1,053.4659   $1,053.47   $1,053.50   $1,053.40