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 $246.41   6.740%   $263.018   $263.02   $263.00   $263.00  
  Purchase #2 $234.45   7.168%   $251.2554   $251.26   $251.25   $251.30  
  Purchase #3 $31.82   6.798%   $33.9831   $33.98   $34.00   $34.00  
  Purchase #4 $231.84   4.520%   $242.3192   $242.32   $242.30   $242.30  
  Purchase #5 $106.69   6.781%   $113.9246   $113.92   $113.90   $113.90  
  Purchase #6 $84.29   7.825%   $90.8857   $90.89   $90.90   $90.90  
  Purchase #7 $113.76   7.267%   $122.0269   $122.03   $122.05   $122.00  
  7 purchase totals = $1,049.26       $1,117.4129   $1,117.42   $1,117.40   $1,117.40