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 $232.63   6.309%   $247.3066   $247.31   $247.30   $247.30  
  Purchase #2 $55.92   10.595%   $61.8447   $61.84   $61.85   $61.80  
  Purchase #3 $121.25   11.485%   $135.1756   $135.18   $135.20   $135.20  
  Purchase #4 $64.47   8.667%   $70.0576   $70.06   $70.05   $70.10  
  Purchase #5 $226.37   11.367%   $252.1015   $252.10   $252.10   $252.10  
  Purchase #6 $152.89   6.150%   $162.2927   $162.29   $162.30   $162.30  
  Purchase #7 $248.45   9.220%   $271.3571   $271.36   $271.35   $271.40  
  7 purchase totals = $1,101.98       $1,200.1358   $1,200.14   $1,200.15   $1,200.20