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 $240.36   6.775%   $256.6444   $256.64   $256.65   $256.60  
  Purchase #2 $182.51   11.334%   $203.1957   $203.20   $203.20   $203.20  
  Purchase #3 $24.64   4.259%   $25.6894   $25.69   $25.70   $25.70  
  Purchase #4 $134.32   9.741%   $147.4041   $147.40   $147.40   $147.40  
  Purchase #5 $159.50   9.134%   $174.0687   $174.07   $174.05   $174.10  
  Purchase #6 $62.80   13.404%   $71.2177   $71.22   $71.20   $71.20  
  Purchase #7 $56.80   13.658%   $64.5577   $64.56   $64.55   $64.60  
  7 purchase totals = $860.93       $942.7777   $942.78   $942.75   $942.80