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 $224.56   10.221%   $247.5123   $247.51   $247.50   $247.50  
  Purchase #2 $185.38   9.512%   $203.0133   $203.01   $203.00   $203.00  
  Purchase #3 $208.60   7.221%   $223.663   $223.66   $223.65   $223.70  
  Purchase #4 $40.59   8.436%   $44.0142   $44.01   $44.00   $44.00  
  Purchase #5 $68.70   12.692%   $77.4194   $77.42   $77.40   $77.40  
  Purchase #6 $245.78   7.424%   $264.0267   $264.03   $264.05   $264.00  
  Purchase #7 $10.45   5.469%   $11.0215   $11.02   $11.00   $11.00  
  7 purchase totals = $984.06       $1,070.6704   $1,070.66   $1,070.60   $1,070.60