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 $228.68   5.229%   $240.6377   $240.64   $240.65   $240.60  
  Purchase #2 $55.56   11.114%   $61.7349   $61.73   $61.75   $61.70  
  Purchase #3 $231.59   11.215%   $257.5628   $257.56   $257.55   $257.60  
  Purchase #4 $142.59   6.103%   $151.2923   $151.29   $151.30   $151.30  
  Purchase #5 $238.33   10.660%   $263.736   $263.74   $263.75   $263.70  
  Purchase #6 $247.51   11.685%   $276.4315   $276.43   $276.45   $276.40  
  Purchase #7 $39.53   9.507%   $43.2881   $43.29   $43.30   $43.30  
  7 purchase totals = $1,183.79       $1,294.6833   $1,294.68   $1,294.75   $1,294.60