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 $152.57   10.771%   $169.0033   $169.00   $169.00   $169.00  
  Purchase #2 $57.76   12.744%   $65.1209   $65.12   $65.10   $65.10  
  Purchase #3 $22.85   10.689%   $25.2924   $25.29   $25.30   $25.30  
  Purchase #4 $245.63   4.108%   $255.7205   $255.72   $255.70   $255.70  
  Purchase #5 $209.52   6.751%   $223.6647   $223.66   $223.65   $223.70  
  Purchase #6 $154.57   8.389%   $167.5369   $167.54   $167.55   $167.50  
  Purchase #7 $153.62   3.291%   $158.6756   $158.68   $158.70   $158.70  
  7 purchase totals = $996.52       $1,065.0143   $1,065.01   $1,065.00   $1,065.00