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 $32.27   6.118%   $34.2443   $34.24   $34.25   $34.20  
  Purchase #2 $206.37   11.738%   $230.5937   $230.59   $230.60   $230.60  
  Purchase #3 $50.64   5.520%   $53.4353   $53.44   $53.45   $53.40  
  Purchase #4 $11.51   8.757%   $12.5179   $12.52   $12.50   $12.50  
  Purchase #5 $177.97   11.235%   $197.9649   $197.96   $197.95   $198.00  
  Purchase #6 $98.50   4.146%   $102.5838   $102.58   $102.60   $102.60  
  Purchase #7 $107.43   9.801%   $117.9592   $117.96   $117.95   $118.00  
  7 purchase totals = $684.69       $749.2991   $749.29   $749.30   $749.30