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 $226.75   3.332%   $234.3053   $234.31   $234.30   $234.30  
  Purchase #2 $175.55   5.178%   $184.64   $184.64   $184.65   $184.60  
  Purchase #3 $84.62   9.137%   $92.3517   $92.35   $92.35   $92.40  
  Purchase #4 $231.65   8.599%   $251.5696   $251.57   $251.55   $251.60  
  Purchase #5 $233.98   11.355%   $260.5484   $260.55   $260.55   $260.50  
  Purchase #6 $114.43   7.516%   $123.0306   $123.03   $123.05   $123.00  
  Purchase #7 $175.64   6.281%   $186.6719   $186.67   $186.65   $186.70  
  7 purchase totals = $1,242.62       $1,333.1175   $1,333.12   $1,333.10   $1,333.10