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 $236.50   3.611%   $245.04   $245.04   $245.05   $245.00  
  Purchase #2 $137.43   3.471%   $142.2002   $142.20   $142.20   $142.20  
  Purchase #3 $204.49   11.512%   $228.0309   $228.03   $228.05   $228.00  
  Purchase #4 $250.70   12.523%   $282.0952   $282.10   $282.10   $282.10  
  Purchase #5 $32.55   7.761%   $35.0762   $35.08   $35.10   $35.10  
  Purchase #6 $58.31   12.397%   $65.5387   $65.54   $65.55   $65.50  
  Purchase #7 $22.72   12.454%   $25.5495   $25.55   $25.55   $25.50  
  7 purchase totals = $942.70       $1,023.5307   $1,023.54   $1,023.60   $1,023.40