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 $55.98   8.347%   $60.6527   $60.65   $60.65   $60.70  
  Purchase #2 $87.51   11.370%   $97.4599   $97.46   $97.45   $97.50  
  Purchase #3 $124.52   13.835%   $141.7473   $141.75   $141.75   $141.70  
  Purchase #4 $241.99   8.417%   $262.3583   $262.36   $262.35   $262.40  
  Purchase #5 $242.99   3.647%   $251.8518   $251.85   $251.85   $251.90  
  Purchase #6 $161.83   7.655%   $174.2181   $174.22   $174.20   $174.20  
  Purchase #7 $138.54   11.823%   $154.9196   $154.92   $154.90   $154.90  
  7 purchase totals = $1,053.36       $1,143.2077   $1,143.21   $1,143.15   $1,143.30