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 $140.84   10.738%   $155.9634   $155.96   $155.95   $156.00  
  Purchase #2 $89.85   13.369%   $101.862   $101.86   $101.85   $101.90  
  Purchase #3 $209.36   12.205%   $234.9124   $234.91   $234.90   $234.90  
  Purchase #4 $224.78   10.591%   $248.5864   $248.59   $248.60   $248.60  
  Purchase #5 $150.86   8.268%   $163.3331   $163.33   $163.35   $163.30  
  Purchase #6 $181.95   5.318%   $191.6261   $191.63   $191.65   $191.60  
  Purchase #7 $55.58   9.793%   $61.0229   $61.02   $61.00   $61.00  
  7 purchase totals = $1,053.22       $1,157.3063   $1,157.30   $1,157.30   $1,157.30