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 $118.74   13.658%   $134.9575   $134.96   $134.95   $135.00  
  Purchase #2 $120.63   11.247%   $134.1973   $134.20   $134.20   $134.20  
  Purchase #3 $250.61   6.608%   $267.1703   $267.17   $267.15   $267.20  
  Purchase #4 $121.59   9.291%   $132.8869   $132.89   $132.90   $132.90  
  Purchase #5 $201.86   13.261%   $228.6287   $228.63   $228.65   $228.60  
  Purchase #6 $98.48   9.466%   $107.8021   $107.80   $107.80   $107.80  
  Purchase #7 $42.75   13.539%   $48.5379   $48.54   $48.55   $48.50  
  7 purchase totals = $954.66       $1,054.1807   $1,054.19   $1,054.20   $1,054.20