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 $39.66   11.173%   $44.0912   $44.09   $44.10   $44.10  
  Purchase #2 $194.49   13.114%   $219.9954   $220.00   $220.00   $220.00  
  Purchase #3 $209.90   12.417%   $235.9633   $235.96   $235.95   $236.00  
  Purchase #4 $225.42   13.138%   $255.0357   $255.04   $255.05   $255.00  
  Purchase #5 $160.74   8.266%   $174.0268   $174.03   $174.05   $174.00  
  Purchase #6 $217.82   6.723%   $232.464   $232.46   $232.45   $232.50  
  Purchase #7 $40.25   5.165%   $42.3289   $42.33   $42.35   $42.30  
  7 purchase totals = $1,088.28       $1,203.9053   $1,203.91   $1,203.95   $1,203.90