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 $248.80   13.726%   $282.9503   $282.95   $282.95   $283.00  
  Purchase #2 $77.93   4.303%   $81.2833   $81.28   $81.30   $81.30  
  Purchase #3 $63.77   9.829%   $70.038   $70.04   $70.05   $70.00  
  Purchase #4 $79.30   9.708%   $86.9984   $87.00   $87.00   $87.00  
  Purchase #5 $194.35   8.714%   $211.2857   $211.29   $211.30   $211.30  
  Purchase #6 $89.55   7.342%   $96.1248   $96.12   $96.10   $96.10  
  Purchase #7 $160.64   13.194%   $181.8348   $181.83   $181.85   $181.80  
  7 purchase totals = $914.34       $1,010.5153   $1,010.51   $1,010.55   $1,010.50