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 $158.34   12.831%   $178.6566   $178.66   $178.65   $178.70  
  Purchase #2 $88.79   3.274%   $91.697   $91.70   $91.70   $91.70  
  Purchase #3 $151.78   5.831%   $160.6303   $160.63   $160.65   $160.60  
  Purchase #4 $214.91   13.150%   $243.1707   $243.17   $243.15   $243.20  
  Purchase #5 $195.80   11.159%   $217.6493   $217.65   $217.65   $217.60  
  Purchase #6 $239.30   13.493%   $271.5887   $271.59   $271.60   $271.60  
  Purchase #7 $93.42   13.437%   $105.9728   $105.97   $105.95   $106.00  
  7 purchase totals = $1,142.34       $1,269.3654   $1,269.37   $1,269.35   $1,269.40