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 $97.52   9.342%   $106.6303   $106.63   $106.65   $106.60  
  Purchase #2 $239.85   4.191%   $249.9021   $249.90   $249.90   $249.90  
  Purchase #3 $50.39   3.148%   $51.9763   $51.98   $52.00   $52.00  
  Purchase #4 $242.52   10.530%   $268.0574   $268.06   $268.05   $268.10  
  Purchase #5 $75.55   13.482%   $85.7357   $85.74   $85.75   $85.70  
  Purchase #6 $119.44   9.634%   $130.9468   $130.95   $130.95   $130.90  
  Purchase #7 $117.98   5.546%   $124.5232   $124.52   $124.50   $124.50  
  7 purchase totals = $943.25       $1,017.7718   $1,017.78   $1,017.80   $1,017.70