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 $60.74   13.786%   $69.1136   $69.11   $69.10   $69.10  
  Purchase #2 $245.95   12.401%   $276.4503   $276.45   $276.45   $276.50  
  Purchase #3 $229.81   8.480%   $249.2979   $249.30   $249.30   $249.30  
  Purchase #4 $66.74   6.811%   $71.2857   $71.29   $71.30   $71.30  
  Purchase #5 $156.51   5.757%   $165.5203   $165.52   $165.50   $165.50  
  Purchase #6 $152.75   4.325%   $159.3564   $159.36   $159.35   $159.40  
  Purchase #7 $195.53   12.683%   $220.3291   $220.33   $220.35   $220.30  
  7 purchase totals = $1,108.03       $1,211.3533   $1,211.36   $1,211.35   $1,211.40