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 $151.83   7.591%   $163.3554   $163.36   $163.35   $163.40  
  Purchase #2 $218.77   6.417%   $232.8085   $232.81   $232.80   $232.80  
  Purchase #3 $52.38   3.686%   $54.3107   $54.31   $54.30   $54.30  
  Purchase #4 $138.62   10.808%   $153.602   $153.60   $153.60   $153.60  
  Purchase #5 $232.91   3.432%   $240.9035   $240.90   $240.90   $240.90  
  Purchase #6 $232.93   3.211%   $240.4094   $240.41   $240.40   $240.40  
  Purchase #7 $172.33   5.464%   $181.7461   $181.75   $181.75   $181.70  
  7 purchase totals = $1,199.77       $1,267.1356   $1,267.14   $1,267.10   $1,267.10