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 $60.58   11.754%   $67.7006   $67.70   $67.70   $67.70  
  Purchase #2 $57.78   13.850%   $65.7825   $65.78   $65.80   $65.80  
  Purchase #3 $12.52   12.372%   $14.069   $14.07   $14.05   $14.10  
  Purchase #4 $201.54   12.656%   $227.0469   $227.05   $227.05   $227.00  
  Purchase #5 $160.32   4.663%   $167.7957   $167.80   $167.80   $167.80  
  Purchase #6 $118.91   10.111%   $130.933   $130.93   $130.95   $130.90  
  Purchase #7 $58.99   11.449%   $65.7438   $65.74   $65.75   $65.70  
  7 purchase totals = $670.64       $739.0715   $739.07   $739.10   $739.00