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 $16.96   13.862%   $19.311   $19.31   $19.30   $19.30  
  Purchase #2 $150.87   9.124%   $164.6354   $164.64   $164.65   $164.60  
  Purchase #3 $154.67   5.234%   $162.7654   $162.77   $162.75   $162.80  
  Purchase #4 $98.58   8.312%   $106.774   $106.77   $106.75   $106.80  
  Purchase #5 $204.40   8.357%   $221.4817   $221.48   $221.50   $221.50  
  Purchase #6 $189.64   8.774%   $206.279   $206.28   $206.30   $206.30  
  Purchase #7 $134.92   12.174%   $151.3452   $151.35   $151.35   $151.30  
  7 purchase totals = $950.04       $1,032.5917   $1,032.60   $1,032.60   $1,032.60