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 $39.84   9.264%   $43.5308   $43.53   $43.55   $43.50  
  Purchase #2 $60.68   10.356%   $66.964   $66.96   $66.95   $67.00  
  Purchase #3 $141.53   12.426%   $159.1165   $159.12   $159.10   $159.10  
  Purchase #4 $217.96   13.129%   $246.576   $246.58   $246.60   $246.60  
  Purchase #5 $25.86   3.235%   $26.6966   $26.70   $26.70   $26.70  
  Purchase #6 $198.44   6.113%   $210.5706   $210.57   $210.55   $210.60  
  Purchase #7 $138.91   11.747%   $155.2278   $155.23   $155.25   $155.20  
  7 purchase totals = $823.22       $908.6823   $908.69   $908.70   $908.70