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 $31.80   6.754%   $33.9478   $33.95   $33.95   $33.90  
  Purchase #2 $122.64   6.785%   $130.9611   $130.96   $130.95   $131.00  
  Purchase #3 $196.37   6.668%   $209.464   $209.46   $209.45   $209.50  
  Purchase #4 $149.27   12.734%   $168.278   $168.28   $168.30   $168.30  
  Purchase #5 $122.26   4.399%   $127.6382   $127.64   $127.65   $127.60  
  Purchase #6 $170.83   8.277%   $184.9696   $184.97   $184.95   $185.00  
  Purchase #7 $166.39   4.538%   $173.9408   $173.94   $173.95   $173.90  
  7 purchase totals = $959.56       $1,029.1995   $1,029.20   $1,029.20   $1,029.20