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 $53.70   13.550%   $60.9764   $60.98   $61.00   $61.00  
  Purchase #2 $205.51   6.615%   $219.1045   $219.10   $219.10   $219.10  
  Purchase #3 $174.55   7.382%   $187.4353   $187.44   $187.45   $187.40  
  Purchase #4 $186.47   7.536%   $200.5224   $200.52   $200.50   $200.50  
  Purchase #5 $20.93   13.162%   $23.6848   $23.68   $23.70   $23.70  
  Purchase #6 $133.58   11.163%   $148.4915   $148.49   $148.50   $148.50  
  Purchase #7 $233.48   5.237%   $245.7073   $245.71   $245.70   $245.70  
  7 purchase totals = $1,008.22       $1,085.9222   $1,085.92   $1,085.95   $1,085.90