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 $118.81   13.231%   $134.5298   $134.53   $134.55   $134.50  
  Purchase #2 $95.57   11.754%   $106.8033   $106.80   $106.80   $106.80  
  Purchase #3 $167.39   13.373%   $189.7751   $189.78   $189.80   $189.80  
  Purchase #4 $239.75   9.503%   $262.5334   $262.53   $262.55   $262.50  
  Purchase #5 $40.98   7.519%   $44.0613   $44.06   $44.05   $44.10  
  Purchase #6 $198.90   5.505%   $209.8494   $209.85   $209.85   $209.80  
  Purchase #7 $70.70   4.296%   $73.7373   $73.74   $73.75   $73.70  
  7 purchase totals = $932.10       $1,021.2896   $1,021.29   $1,021.35   $1,021.20