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 $180.65   6.612%   $192.5946   $192.59   $192.60   $192.60  
  Purchase #2 $68.45   3.184%   $70.6294   $70.63   $70.65   $70.60  
  Purchase #3 $27.35   7.713%   $29.4595   $29.46   $29.45   $29.50  
  Purchase #4 $209.41   13.448%   $237.5715   $237.57   $237.55   $237.60  
  Purchase #5 $74.60   5.578%   $78.7612   $78.76   $78.75   $78.80  
  Purchase #6 $54.48   4.800%   $57.095   $57.10   $57.10   $57.10  
  Purchase #7 $87.59   8.462%   $95.0019   $95.00   $95.00   $95.00  
  7 purchase totals = $702.53       $761.1131   $761.11   $761.10   $761.20