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 $210.88   13.774%   $239.9266   $239.93   $239.95   $239.90  
  Purchase #2 $246.73   11.307%   $274.6278   $274.63   $274.65   $274.60  
  Purchase #3 $196.96   13.700%   $223.9435   $223.94   $223.95   $223.90  
  Purchase #4 $52.30   7.138%   $56.0332   $56.03   $56.05   $56.00  
  Purchase #5 $86.25   6.582%   $91.927   $91.93   $91.95   $91.90  
  Purchase #6 $225.98   11.423%   $251.7937   $251.79   $251.80   $251.80  
  Purchase #7 $44.54   12.729%   $50.2095   $50.21   $50.20   $50.20  
  7 purchase totals = $1,063.64       $1,188.4613   $1,188.46   $1,188.55   $1,188.30