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 $162.95   8.784%   $177.2635   $177.26   $177.25   $177.30  
  Purchase #2 $100.96   12.793%   $113.8758   $113.88   $113.90   $113.90  
  Purchase #3 $196.94   10.538%   $217.6935   $217.69   $217.70   $217.70  
  Purchase #4 $209.74   7.115%   $224.663   $224.66   $224.65   $224.70  
  Purchase #5 $65.75   10.791%   $72.8451   $72.85   $72.85   $72.80  
  Purchase #6 $137.70   11.192%   $153.1114   $153.11   $153.10   $153.10  
  Purchase #7 $199.73   11.806%   $223.3101   $223.31   $223.30   $223.30  
  7 purchase totals = $1,073.77       $1,182.7624   $1,182.76   $1,182.75   $1,182.80