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 $158.60   9.448%   $173.5845   $173.58   $173.60   $173.60  
  Purchase #2 $211.98   6.472%   $225.6993   $225.70   $225.70   $225.70  
  Purchase #3 $16.45   8.594%   $17.8637   $17.86   $17.85   $17.90  
  Purchase #4 $180.93   12.470%   $203.492   $203.49   $203.50   $203.50  
  Purchase #5 $210.72   4.558%   $220.3246   $220.32   $220.30   $220.30  
  Purchase #6 $125.66   12.124%   $140.895   $140.90   $140.90   $140.90  
  Purchase #7 $126.82   7.262%   $136.0297   $136.03   $136.05   $136.00  
  7 purchase totals = $1,031.16       $1,117.8888   $1,117.88   $1,117.90   $1,117.90