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 $55.90   9.460%   $61.1881   $61.19   $61.20   $61.20  
  Purchase #2 $184.66   7.736%   $198.9453   $198.95   $198.95   $198.90  
  Purchase #3 $91.36   6.384%   $97.1924   $97.19   $97.20   $97.20  
  Purchase #4 $210.55   9.731%   $231.0386   $231.04   $231.05   $231.00  
  Purchase #5 $120.42   9.225%   $131.5287   $131.53   $131.55   $131.50  
  Purchase #6 $48.40   12.289%   $54.3479   $54.35   $54.35   $54.30  
  Purchase #7 $235.96   5.357%   $248.6004   $248.60   $248.60   $248.60  
  7 purchase totals = $947.25       $1,022.8414   $1,022.85   $1,022.90   $1,022.70