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 $187.56   9.314%   $205.0293   $205.03   $205.05   $205.00  
  Purchase #2 $214.46   8.521%   $232.7341   $232.73   $232.75   $232.70  
  Purchase #3 $37.46   11.218%   $41.6623   $41.66   $41.65   $41.70  
  Purchase #4 $195.78   11.246%   $217.7974   $217.80   $217.80   $217.80  
  Purchase #5 $173.75   4.414%   $181.4193   $181.42   $181.40   $181.40  
  Purchase #6 $38.38   12.278%   $43.0923   $43.09   $43.10   $43.10  
  Purchase #7 $85.59   12.203%   $96.0345   $96.03   $96.05   $96.00  
  7 purchase totals = $932.98       $1,017.7692   $1,017.76   $1,017.80   $1,017.70