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 $244.76   3.262%   $252.7441   $252.74   $252.75   $252.70  
  Purchase #2 $140.67   11.425%   $156.7415   $156.74   $156.75   $156.70  
  Purchase #3 $65.75   9.302%   $71.8661   $71.87   $71.85   $71.90  
  Purchase #4 $124.74   9.108%   $136.1013   $136.10   $136.10   $136.10  
  Purchase #5 $9.29   3.339%   $9.6002   $9.60   $9.60   $9.60  
  Purchase #6 $170.47   13.777%   $193.9557   $193.96   $193.95   $194.00  
  Purchase #7 $198.94   12.450%   $223.708   $223.71   $223.70   $223.70  
  7 purchase totals = $954.62       $1,044.7169   $1,044.72   $1,044.70   $1,044.70