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 $24.43   3.156%   $25.201   $25.20   $25.20   $25.20  
  Purchase #2 $215.95   8.614%   $234.5519   $234.55   $234.55   $234.60  
  Purchase #3 $191.69   3.547%   $198.4892   $198.49   $198.50   $198.50  
  Purchase #4 $204.36   7.491%   $219.6686   $219.67   $219.65   $219.70  
  Purchase #5 $116.65   12.320%   $131.0213   $131.02   $131.00   $131.00  
  Purchase #6 $167.65   10.199%   $184.7486   $184.75   $184.75   $184.70  
  Purchase #7 $39.45   8.289%   $42.72   $42.72   $42.70   $42.70  
  7 purchase totals = $960.18       $1,036.4006   $1,036.40   $1,036.35   $1,036.40