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 $5.59   11.822%   $6.2508   $6.25   $6.25   $6.30  
  Purchase #2 $249.81   7.423%   $268.3534   $268.35   $268.35   $268.40  
  Purchase #3 $194.25   13.124%   $219.7434   $219.74   $219.75   $219.70  
  Purchase #4 $45.75   5.324%   $48.1857   $48.19   $48.20   $48.20  
  Purchase #5 $243.45   4.162%   $253.5824   $253.58   $253.60   $253.60  
  Purchase #6 $184.74   10.153%   $203.4967   $203.50   $203.50   $203.50  
  Purchase #7 $161.27   3.531%   $166.9644   $166.96   $166.95   $167.00  
  7 purchase totals = $1,084.86       $1,166.5768   $1,166.57   $1,166.60   $1,166.70