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 $203.53   5.418%   $214.5573   $214.56   $214.55   $214.60  
  Purchase #2 $187.70   4.390%   $195.94   $195.94   $195.95   $195.90  
  Purchase #3 $238.69   11.708%   $266.6358   $266.64   $266.65   $266.60  
  Purchase #4 $241.88   13.759%   $275.1603   $275.16   $275.15   $275.20  
  Purchase #5 $197.50   13.841%   $224.836   $224.84   $224.85   $224.80  
  Purchase #6 $203.96   7.588%   $219.4365   $219.44   $219.45   $219.40  
  Purchase #7 $98.30   4.865%   $103.0823   $103.08   $103.10   $103.10  
  7 purchase totals = $1,371.56       $1,499.6482   $1,499.66   $1,499.70   $1,499.60