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 $39.92   11.471%   $44.4992   $44.50   $44.50   $44.50  
  Purchase #2 $246.81   8.847%   $268.6453   $268.65   $268.65   $268.60  
  Purchase #3 $168.53   8.306%   $182.5281   $182.53   $182.55   $182.50  
  Purchase #4 $183.63   11.199%   $204.1947   $204.19   $204.20   $204.20  
  Purchase #5 $135.38   8.657%   $147.0998   $147.10   $147.10   $147.10  
  Purchase #6 $21.94   7.479%   $23.5809   $23.58   $23.60   $23.60  
  Purchase #7 $181.51   7.153%   $194.4934   $194.49   $194.50   $194.50  
  7 purchase totals = $977.72       $1,065.0414   $1,065.04   $1,065.10   $1,065.00