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 $162.75   13.867%   $185.3185   $185.32   $185.30   $185.30  
  Purchase #2 $9.47   10.386%   $10.4536   $10.45   $10.45   $10.50  
  Purchase #3 $22.45   9.776%   $24.6447   $24.64   $24.65   $24.60  
  Purchase #4 $59.68   6.528%   $63.5759   $63.58   $63.60   $63.60  
  Purchase #5 $232.51   4.797%   $243.6635   $243.66   $243.65   $243.70  
  Purchase #6 $89.65   6.418%   $95.4037   $95.40   $95.40   $95.40  
  Purchase #7 $174.35   6.232%   $185.2155   $185.22   $185.20   $185.20  
  7 purchase totals = $750.86       $808.2754   $808.27   $808.25   $808.30