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 $53.70   12.618%   $60.4759   $60.48   $60.50   $60.50  
  Purchase #2 $83.97   3.313%   $86.7519   $86.75   $86.75   $86.80  
  Purchase #3 $114.31   9.834%   $125.5512   $125.55   $125.55   $125.60  
  Purchase #4 $166.79   4.754%   $174.7192   $174.72   $174.70   $174.70  
  Purchase #5 $186.99   12.168%   $209.7429   $209.74   $209.75   $209.70  
  Purchase #6 $128.63   10.327%   $141.9136   $141.91   $141.90   $141.90  
  Purchase #7 $203.52   8.475%   $220.7683   $220.77   $220.75   $220.80  
  7 purchase totals = $937.91       $1,019.9230   $1,019.92   $1,019.90   $1,020.00