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 $231.49   12.597%   $260.6508   $260.65   $260.65   $260.70  
  Purchase #2 $171.28   3.457%   $177.2011   $177.20   $177.20   $177.20  
  Purchase #3 $147.26   10.631%   $162.9152   $162.92   $162.90   $162.90  
  Purchase #4 $52.43   3.541%   $54.2865   $54.29   $54.30   $54.30  
  Purchase #5 $195.47   3.755%   $202.8099   $202.81   $202.80   $202.80  
  Purchase #6 $227.84   3.111%   $234.9281   $234.93   $234.95   $234.90  
  Purchase #7 $240.64   13.270%   $272.5729   $272.57   $272.55   $272.60  
  7 purchase totals = $1,266.41       $1,365.3645   $1,365.37   $1,365.35   $1,365.40