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 $61.92   12.363%   $69.5752   $69.58   $69.60   $69.60  
  Purchase #2 $24.78   10.108%   $27.2848   $27.28   $27.30   $27.30  
  Purchase #3 $230.31   12.333%   $258.7141   $258.71   $258.70   $258.70  
  Purchase #4 $230.50   12.574%   $259.4831   $259.48   $259.50   $259.50  
  Purchase #5 $241.38   4.665%   $252.6404   $252.64   $252.65   $252.60  
  Purchase #6 $12.66   7.415%   $13.5987   $13.60   $13.60   $13.60  
  Purchase #7 $158.82   10.503%   $175.5009   $175.50   $175.50   $175.50  
  7 purchase totals = $960.37       $1,056.7972   $1,056.79   $1,056.85   $1,056.80