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 $247.46   11.553%   $276.0491   $276.05   $276.05   $276.00  
  Purchase #2 $100.85   7.764%   $108.68   $108.68   $108.70   $108.70  
  Purchase #3 $200.29   12.549%   $225.4244   $225.42   $225.40   $225.40  
  Purchase #4 $92.58   11.164%   $102.9156   $102.92   $102.90   $102.90  
  Purchase #5 $30.90   5.767%   $32.682   $32.68   $32.70   $32.70  
  Purchase #6 $68.91   10.349%   $76.0415   $76.04   $76.05   $76.00  
  Purchase #7 $175.56   12.631%   $197.735   $197.74   $197.75   $197.70  
  7 purchase totals = $916.55       $1,019.5276   $1,019.53   $1,019.55   $1,019.40