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 $188.47   9.531%   $206.4331   $206.43   $206.45   $206.40  
  Purchase #2 $93.43   12.310%   $104.9312   $104.93   $104.95   $104.90  
  Purchase #3 $8.82   7.261%   $9.4604   $9.46   $9.45   $9.50  
  Purchase #4 $12.93   5.823%   $13.6829   $13.68   $13.70   $13.70  
  Purchase #5 $211.69   13.618%   $240.5179   $240.52   $240.50   $240.50  
  Purchase #6 $233.84   6.316%   $248.6093   $248.61   $248.60   $248.60  
  Purchase #7 $220.44   5.864%   $233.3666   $233.37   $233.35   $233.40  
  7 purchase totals = $969.62       $1,057.0014   $1,057.00   $1,057.00   $1,057.00