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 $96.58   6.157%   $102.5264   $102.53   $102.55   $102.50  
  Purchase #2 $220.45   9.738%   $241.9174   $241.92   $241.90   $241.90  
  Purchase #3 $249.69   11.419%   $278.2021   $278.20   $278.20   $278.20  
  Purchase #4 $166.86   13.721%   $189.7549   $189.75   $189.75   $189.80  
  Purchase #5 $30.59   12.306%   $34.3544   $34.35   $34.35   $34.40  
  Purchase #6 $166.88   4.710%   $174.74   $174.74   $174.75   $174.70  
  Purchase #7 $90.80   9.409%   $99.3434   $99.34   $99.35   $99.30  
  7 purchase totals = $1,021.85       $1,120.8386   $1,120.83   $1,120.85   $1,120.80