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 $30.86   11.456%   $34.3953   $34.40   $34.40   $34.40  
  Purchase #2 $213.92   3.533%   $221.4778   $221.48   $221.50   $221.50  
  Purchase #3 $83.33   4.679%   $87.229   $87.23   $87.25   $87.20  
  Purchase #4 $195.58   8.145%   $211.51   $211.51   $211.50   $211.50  
  Purchase #5 $54.61   9.196%   $59.6319   $59.63   $59.65   $59.60  
  Purchase #6 $147.44   11.505%   $164.403   $164.40   $164.40   $164.40  
  Purchase #7 $196.67   3.645%   $203.8386   $203.84   $203.85   $203.80  
  7 purchase totals = $922.41       $982.4856   $982.49   $982.55   $982.40