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 $77.47   11.405%   $86.3055   $86.31   $86.30   $86.30  
  Purchase #2 $23.55   5.409%   $24.8238   $24.82   $24.80   $24.80  
  Purchase #3 $217.67   9.852%   $239.1148   $239.11   $239.10   $239.10  
  Purchase #4 $173.40   13.275%   $196.4189   $196.42   $196.40   $196.40  
  Purchase #5 $149.96   9.584%   $164.3322   $164.33   $164.35   $164.30  
  Purchase #6 $88.80   6.246%   $94.3464   $94.35   $94.35   $94.30  
  Purchase #7 $195.57   11.168%   $217.4113   $217.41   $217.40   $217.40  
  7 purchase totals = $926.42       $1,022.7529   $1,022.75   $1,022.70   $1,022.60