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 $61.88   10.712%   $68.5086   $68.51   $68.50   $68.50  
  Purchase #2 $250.30   7.614%   $269.3578   $269.36   $269.35   $269.40  
  Purchase #3 $214.33   7.740%   $230.9191   $230.92   $230.90   $230.90  
  Purchase #4 $156.64   3.624%   $162.3166   $162.32   $162.30   $162.30  
  Purchase #5 $187.52   4.165%   $195.3302   $195.33   $195.35   $195.30  
  Purchase #6 $74.33   13.613%   $84.4485   $84.45   $84.45   $84.40  
  Purchase #7 $241.87   8.743%   $263.0167   $263.02   $263.00   $263.00  
  7 purchase totals = $1,186.87       $1,273.8975   $1,273.91   $1,273.85   $1,273.80