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 $27.94   4.661%   $29.2423   $29.24   $29.25   $29.20  
  Purchase #2 $228.35   3.195%   $235.6458   $235.65   $235.65   $235.60  
  Purchase #3 $239.31   10.635%   $264.7606   $264.76   $264.75   $264.80  
  Purchase #4 $50.83   3.276%   $52.4952   $52.50   $52.50   $52.50  
  Purchase #5 $164.88   11.272%   $183.4653   $183.47   $183.45   $183.50  
  Purchase #6 $165.80   11.470%   $184.8173   $184.82   $184.80   $184.80  
  Purchase #7 $62.70   10.237%   $69.1186   $69.12   $69.10   $69.10  
  7 purchase totals = $939.81       $1,019.5451   $1,019.56   $1,019.50   $1,019.50