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 $58.56   12.579%   $65.9263   $65.93   $65.95   $65.90  
  Purchase #2 $249.64   12.562%   $280.9998   $281.00   $281.00   $281.00  
  Purchase #3 $177.52   7.215%   $190.3281   $190.33   $190.35   $190.30  
  Purchase #4 $226.46   10.253%   $249.6789   $249.68   $249.70   $249.70  
  Purchase #5 $222.60   3.681%   $230.7939   $230.79   $230.80   $230.80  
  Purchase #6 $244.77   8.264%   $264.9978   $265.00   $265.00   $265.00  
  Purchase #7 $135.30   12.221%   $151.835   $151.84   $151.85   $151.80  
  7 purchase totals = $1,314.85       $1,434.5598   $1,434.57   $1,434.65   $1,434.50