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 $88.90   4.348%   $92.7654   $92.77   $92.75   $92.80  
  Purchase #2 $231.32   8.861%   $251.8173   $251.82   $251.80   $251.80  
  Purchase #3 $167.80   8.623%   $182.2694   $182.27   $182.25   $182.30  
  Purchase #4 $146.46   4.319%   $152.7856   $152.79   $152.80   $152.80  
  Purchase #5 $22.32   6.277%   $23.721   $23.72   $23.70   $23.70  
  Purchase #6 $77.39   11.270%   $86.1119   $86.11   $86.10   $86.10  
  Purchase #7 $204.52   6.296%   $217.3966   $217.40   $217.40   $217.40  
  7 purchase totals = $938.71       $1,006.8672   $1,006.88   $1,006.80   $1,006.90