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 $61.87   12.686%   $69.7188   $69.72   $69.70   $69.70  
  Purchase #2 $63.43   13.182%   $71.7913   $71.79   $71.80   $71.80  
  Purchase #3 $223.49   11.835%   $249.94   $249.94   $249.95   $249.90  
  Purchase #4 $100.52   11.770%   $112.3512   $112.35   $112.35   $112.40  
  Purchase #5 $174.49   10.218%   $192.3194   $192.32   $192.30   $192.30  
  Purchase #6 $90.86   10.321%   $100.2377   $100.24   $100.25   $100.20  
  Purchase #7 $202.92   13.366%   $230.0423   $230.04   $230.05   $230.00  
  7 purchase totals = $917.58       $1,026.4007   $1,026.40   $1,026.40   $1,026.30