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 $198.78   8.717%   $216.1077   $216.11   $216.10   $216.10  
  Purchase #2 $166.88   9.444%   $182.6401   $182.64   $182.65   $182.60  
  Purchase #3 $236.79   13.823%   $269.5215   $269.52   $269.50   $269.50  
  Purchase #4 $169.33   8.261%   $183.3184   $183.32   $183.30   $183.30  
  Purchase #5 $22.26   12.788%   $25.1066   $25.11   $25.10   $25.10  
  Purchase #6 $88.63   3.260%   $91.5193   $91.52   $91.50   $91.50  
  Purchase #7 $213.94   12.434%   $240.5413   $240.54   $240.55   $240.50  
  7 purchase totals = $1,096.61       $1,208.7549   $1,208.76   $1,208.70   $1,208.60