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 $152.63   6.218%   $162.1205   $162.12   $162.10   $162.10  
  Purchase #2 $50.99   9.587%   $55.8784   $55.88   $55.90   $55.90  
  Purchase #3 $197.53   11.213%   $219.679   $219.68   $219.70   $219.70  
  Purchase #4 $169.40   13.816%   $192.8043   $192.80   $192.80   $192.80  
  Purchase #5 $110.34   8.280%   $119.4762   $119.48   $119.50   $119.50  
  Purchase #6 $237.97   5.606%   $251.3106   $251.31   $251.30   $251.30  
  Purchase #7 $19.35   11.364%   $21.5489   $21.55   $21.55   $21.50  
  7 purchase totals = $938.21       $1,022.8179   $1,022.82   $1,022.85   $1,022.80