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 $216.51   13.806%   $246.4014   $246.40   $246.40   $246.40  
  Purchase #2 $184.44   8.526%   $200.1654   $200.17   $200.15   $200.20  
  Purchase #3 $13.41   8.671%   $14.5728   $14.57   $14.55   $14.60  
  Purchase #4 $45.36   5.483%   $47.8471   $47.85   $47.85   $47.80  
  Purchase #5 $244.71   9.386%   $267.6785   $267.68   $267.70   $267.70  
  Purchase #6 $161.52   7.615%   $173.8197   $173.82   $173.80   $173.80  
  Purchase #7 $75.65   12.297%   $84.9527   $84.95   $84.95   $85.00  
  7 purchase totals = $941.60       $1,035.4376   $1,035.44   $1,035.40   $1,035.50