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 $105.81   10.799%   $117.2364   $117.24   $117.25   $117.20  
  Purchase #2 $232.98   13.638%   $264.7538   $264.75   $264.75   $264.80  
  Purchase #3 $72.75   10.290%   $80.236   $80.24   $80.25   $80.20  
  Purchase #4 $224.85   11.808%   $251.4003   $251.40   $251.40   $251.40  
  Purchase #5 $66.94   5.393%   $70.5501   $70.55   $70.55   $70.60  
  Purchase #6 $100.54   6.441%   $107.0158   $107.02   $107.00   $107.00  
  Purchase #7 $157.75   6.375%   $167.8066   $167.81   $167.80   $167.80  
  7 purchase totals = $961.62       $1,058.9990   $1,059.01   $1,059.00   $1,059.00