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 $233.80   8.845%   $254.4796   $254.48   $254.50   $254.50  
  Purchase #2 $235.38   4.742%   $246.5417   $246.54   $246.55   $246.50  
  Purchase #3 $30.55   10.611%   $33.7917   $33.79   $33.80   $33.80  
  Purchase #4 $136.50   8.313%   $147.8472   $147.85   $147.85   $147.80  
  Purchase #5 $231.29   8.626%   $251.2411   $251.24   $251.25   $251.20  
  Purchase #6 $65.56   4.320%   $68.3922   $68.39   $68.40   $68.40  
  Purchase #7 $41.80   7.289%   $44.8468   $44.85   $44.85   $44.80  
  7 purchase totals = $974.88       $1,047.1403   $1,047.14   $1,047.20   $1,047.00