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 $90.99   6.122%   $96.5604   $96.56   $96.55   $96.60  
  Purchase #2 $212.43   6.809%   $226.8944   $226.89   $226.90   $226.90  
  Purchase #3 $120.37   12.112%   $134.9492   $134.95   $134.95   $134.90  
  Purchase #4 $247.60   10.645%   $273.957   $273.96   $273.95   $274.00  
  Purchase #5 $90.75   6.510%   $96.6578   $96.66   $96.65   $96.70  
  Purchase #6 $78.74   8.386%   $85.3431   $85.34   $85.35   $85.30  
  Purchase #7 $130.48   3.674%   $135.2738   $135.27   $135.25   $135.30  
  7 purchase totals = $971.36       $1,049.6357   $1,049.63   $1,049.60   $1,049.70