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 $61.45   7.562%   $66.0968   $66.10   $66.10   $66.10  
  Purchase #2 $218.78   11.660%   $244.2897   $244.29   $244.30   $244.30  
  Purchase #3 $161.57   7.333%   $173.4179   $173.42   $173.40   $173.40  
  Purchase #4 $100.35   7.734%   $108.1111   $108.11   $108.10   $108.10  
  Purchase #5 $211.67   11.475%   $235.9591   $235.96   $235.95   $236.00  
  Purchase #6 $242.93   12.874%   $274.2048   $274.20   $274.20   $274.20  
  Purchase #7 $186.51   4.384%   $194.6866   $194.69   $194.70   $194.70  
  7 purchase totals = $1,183.26       $1,296.7660   $1,296.77   $1,296.75   $1,296.80