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 $247.49   10.596%   $273.714   $273.71   $273.70   $273.70  
  Purchase #2 $124.90   6.248%   $132.7038   $132.70   $132.70   $132.70  
  Purchase #3 $33.46   12.200%   $37.5421   $37.54   $37.55   $37.50  
  Purchase #4 $62.64   12.388%   $70.3998   $70.40   $70.40   $70.40  
  Purchase #5 $69.90   11.445%   $77.9001   $77.90   $77.90   $77.90  
  Purchase #6 $204.32   7.566%   $219.7789   $219.78   $219.80   $219.80  
  Purchase #7 $197.97   11.135%   $220.014   $220.01   $220.00   $220.00  
  7 purchase totals = $940.68       $1,032.0527   $1,032.04   $1,032.05   $1,032.00