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 $58.52   12.763%   $65.9889   $65.99   $66.00   $66.00  
  Purchase #2 $238.50   5.619%   $251.9013   $251.90   $251.90   $251.90  
  Purchase #3 $238.48   7.229%   $255.7197   $255.72   $255.70   $255.70  
  Purchase #4 $243.59   5.130%   $256.0862   $256.09   $256.10   $256.10  
  Purchase #5 $66.63   5.341%   $70.1887   $70.19   $70.20   $70.20  
  Purchase #6 $94.42   9.481%   $103.372   $103.37   $103.35   $103.40  
  Purchase #7 $23.30   12.347%   $26.1769   $26.18   $26.20   $26.20  
  7 purchase totals = $963.44       $1,029.4337   $1,029.44   $1,029.45   $1,029.50