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 $246.58   8.865%   $268.4393   $268.44   $268.45   $268.40  
  Purchase #2 $234.27   8.736%   $254.7358   $254.74   $254.75   $254.70  
  Purchase #3 $10.97   8.604%   $11.9139   $11.91   $11.90   $11.90  
  Purchase #4 $163.30   6.467%   $173.8606   $173.86   $173.85   $173.90  
  Purchase #5 $211.41   4.808%   $221.5746   $221.57   $221.55   $221.60  
  Purchase #6 $204.91   10.270%   $225.9543   $225.95   $225.95   $226.00  
  Purchase #7 $33.83   9.180%   $36.9356   $36.94   $36.95   $36.90  
  7 purchase totals = $1,105.27       $1,193.4141   $1,193.41   $1,193.40   $1,193.40