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 $68.81   5.612%   $72.6716   $72.67   $72.65   $72.70  
  Purchase #2 $147.53   13.424%   $167.3344   $167.33   $167.35   $167.30  
  Purchase #3 $233.28   7.664%   $251.1586   $251.16   $251.15   $251.20  
  Purchase #4 $162.83   11.717%   $181.9088   $181.91   $181.90   $181.90  
  Purchase #5 $233.63   7.244%   $250.5542   $250.55   $250.55   $250.60  
  Purchase #6 $124.88   7.618%   $134.3934   $134.39   $134.40   $134.40  
  Purchase #7 $152.44   10.507%   $168.4569   $168.46   $168.45   $168.50  
  7 purchase totals = $1,123.40       $1,226.4779   $1,226.47   $1,226.45   $1,226.60