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 $244.77   10.226%   $269.8002   $269.80   $269.80   $269.80  
  Purchase #2 $203.88   3.585%   $211.1891   $211.19   $211.20   $211.20  
  Purchase #3 $239.87   3.162%   $247.4547   $247.45   $247.45   $247.50  
  Purchase #4 $167.27   4.336%   $174.5228   $174.52   $174.50   $174.50  
  Purchase #5 $208.98   11.546%   $233.1088   $233.11   $233.10   $233.10  
  Purchase #6 $13.66   6.392%   $14.5331   $14.53   $14.55   $14.50  
  Purchase #7 $244.28   4.507%   $255.2897   $255.29   $255.30   $255.30  
  7 purchase totals = $1,322.71       $1,405.8984   $1,405.89   $1,405.90   $1,405.90