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 $106.92   8.564%   $116.0766   $116.08   $116.10   $116.10  
  Purchase #2 $232.35   8.440%   $251.9603   $251.96   $251.95   $252.00  
  Purchase #3 $35.77   6.765%   $38.1898   $38.19   $38.20   $38.20  
  Purchase #4 $181.65   3.851%   $188.6453   $188.65   $188.65   $188.60  
  Purchase #5 $243.31   7.737%   $262.1349   $262.13   $262.15   $262.10  
  Purchase #6 $62.87   11.785%   $70.2792   $70.28   $70.30   $70.30  
  Purchase #7 $114.59   5.286%   $120.6472   $120.65   $120.65   $120.60  
  7 purchase totals = $977.46       $1,047.9333   $1,047.94   $1,048.00   $1,047.90