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 $98.42   4.260%   $102.6127   $102.61   $102.60   $102.60  
  Purchase #2 $116.73   4.201%   $121.6338   $121.63   $121.65   $121.60  
  Purchase #3 $134.85   5.320%   $142.024   $142.02   $142.00   $142.00  
  Purchase #4 $141.58   9.747%   $155.3798   $155.38   $155.40   $155.40  
  Purchase #5 $202.48   3.846%   $210.2674   $210.27   $210.25   $210.30  
  Purchase #6 $194.80   11.363%   $216.9351   $216.94   $216.95   $216.90  
  Purchase #7 $77.55   8.297%   $83.9843   $83.98   $84.00   $84.00  
  7 purchase totals = $966.41       $1,032.8371   $1,032.83   $1,032.85   $1,032.80