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 $158.41   11.467%   $176.5749   $176.57   $176.55   $176.60  
  Purchase #2 $196.97   3.419%   $203.7044   $203.70   $203.70   $203.70  
  Purchase #3 $218.79   3.868%   $227.2528   $227.25   $227.25   $227.30  
  Purchase #4 $63.44   9.584%   $69.5201   $69.52   $69.50   $69.50  
  Purchase #5 $214.30   10.453%   $236.7008   $236.70   $236.70   $236.70  
  Purchase #6 $91.80   12.572%   $103.3411   $103.34   $103.35   $103.30  
  Purchase #7 $39.66   4.662%   $41.5089   $41.51   $41.50   $41.50  
  7 purchase totals = $983.37       $1,058.6030   $1,058.59   $1,058.55   $1,058.60