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 $65.92   3.814%   $68.4342   $68.43   $68.45   $68.40  
  Purchase #2 $227.27   6.267%   $241.513   $241.51   $241.50   $241.50  
  Purchase #3 $210.73   9.547%   $230.8484   $230.85   $230.85   $230.80  
  Purchase #4 $147.48   11.232%   $164.045   $164.05   $164.05   $164.00  
  Purchase #5 $14.79   4.129%   $15.4007   $15.40   $15.40   $15.40  
  Purchase #6 $218.72   9.700%   $239.9358   $239.94   $239.95   $239.90  
  Purchase #7 $102.54   5.774%   $108.4607   $108.46   $108.45   $108.50  
  7 purchase totals = $987.45       $1,068.6378   $1,068.64   $1,068.65   $1,068.50