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 $243.55   10.497%   $269.1154   $269.12   $269.10   $269.10  
  Purchase #2 $194.87   8.649%   $211.7243   $211.72   $211.70   $211.70  
  Purchase #3 $44.25   10.688%   $48.9794   $48.98   $49.00   $49.00  
  Purchase #4 $64.84   6.681%   $69.172   $69.17   $69.15   $69.20  
  Purchase #5 $77.43   7.607%   $83.3201   $83.32   $83.30   $83.30  
  Purchase #6 $164.34   8.110%   $177.668   $177.67   $177.65   $177.70  
  Purchase #7 $121.75   12.350%   $136.7861   $136.79   $136.80   $136.80  
  7 purchase totals = $911.03       $996.7653   $996.77   $996.70   $996.80