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 $156.80   10.584%   $173.3957   $173.40   $173.40   $173.40  
  Purchase #2 $222.89   8.440%   $241.7019   $241.70   $241.70   $241.70  
  Purchase #3 $98.73   12.155%   $110.7306   $110.73   $110.75   $110.70  
  Purchase #4 $240.82   11.535%   $268.5986   $268.60   $268.60   $268.60  
  Purchase #5 $48.67   9.495%   $53.2912   $53.29   $53.30   $53.30  
  Purchase #6 $62.75   11.258%   $69.8144   $69.81   $69.80   $69.80  
  Purchase #7 $219.44   5.843%   $232.2619   $232.26   $232.25   $232.30  
  7 purchase totals = $1,050.10       $1,149.7943   $1,149.79   $1,149.80   $1,149.80