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 $250.85   7.199%   $268.9087   $268.91   $268.90   $268.90  
  Purchase #2 $115.91   4.740%   $121.4041   $121.40   $121.40   $121.40  
  Purchase #3 $156.97   7.127%   $168.1573   $168.16   $168.15   $168.20  
  Purchase #4 $41.48   3.462%   $42.916   $42.92   $42.90   $42.90  
  Purchase #5 $191.52   5.742%   $202.5171   $202.52   $202.50   $202.50  
  Purchase #6 $145.86   13.635%   $165.748   $165.75   $165.75   $165.70  
  Purchase #7 $81.76   13.728%   $92.984   $92.98   $93.00   $93.00  
  7 purchase totals = $984.35       $1,062.6352   $1,062.64   $1,062.60   $1,062.60