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 $156.75   13.770%   $178.3345   $178.33   $178.35   $178.30  
  Purchase #2 $220.55   8.440%   $239.1644   $239.16   $239.15   $239.20  
  Purchase #3 $49.54   13.273%   $56.1154   $56.12   $56.10   $56.10  
  Purchase #4 $241.31   9.865%   $265.1152   $265.12   $265.10   $265.10  
  Purchase #5 $50.71   5.542%   $53.5203   $53.52   $53.50   $53.50  
  Purchase #6 $217.60   3.182%   $224.524   $224.52   $224.50   $224.50  
  Purchase #7 $225.64   7.146%   $241.7642   $241.76   $241.75   $241.80  
  7 purchase totals = $1,162.10       $1,258.5380   $1,258.53   $1,258.45   $1,258.50