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 $164.96   7.302%   $177.0054   $177.01   $177.00   $177.00  
  Purchase #2 $7.93   13.596%   $9.0082   $9.01   $9.00   $9.00  
  Purchase #3 $68.76   9.704%   $75.4325   $75.43   $75.45   $75.40  
  Purchase #4 $234.88   7.332%   $252.1014   $252.10   $252.10   $252.10  
  Purchase #5 $26.55   3.816%   $27.5631   $27.56   $27.55   $27.60  
  Purchase #6 $218.89   12.401%   $246.0345   $246.03   $246.05   $246.00  
  Purchase #7 $238.26   12.263%   $267.4778   $267.48   $267.50   $267.50  
  7 purchase totals = $960.23       $1,054.6229   $1,054.62   $1,054.65   $1,054.60