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 $226.36   7.482%   $243.2963   $243.30   $243.30   $243.30  
  Purchase #2 $245.73   9.479%   $269.0227   $269.02   $269.00   $269.00  
  Purchase #3 $14.99   4.565%   $15.6743   $15.67   $15.65   $15.70  
  Purchase #4 $152.50   3.291%   $157.5188   $157.52   $157.50   $157.50  
  Purchase #5 $62.53   9.653%   $68.566   $68.57   $68.55   $68.60  
  Purchase #6 $238.73   7.368%   $256.3196   $256.32   $256.30   $256.30  
  Purchase #7 $56.41   9.873%   $61.9794   $61.98   $62.00   $62.00  
  7 purchase totals = $997.25       $1,072.3771   $1,072.38   $1,072.30   $1,072.40