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 $24.96   5.531%   $26.3405   $26.34   $26.35   $26.30  
  Purchase #2 $43.32   11.306%   $48.2178   $48.22   $48.20   $48.20  
  Purchase #3 $130.56   11.540%   $145.6266   $145.63   $145.65   $145.60  
  Purchase #4 $90.63   9.645%   $99.3713   $99.37   $99.35   $99.40  
  Purchase #5 $203.26   7.814%   $219.1427   $219.14   $219.15   $219.10  
  Purchase #6 $183.94   12.482%   $206.8994   $206.90   $206.90   $206.90  
  Purchase #7 $51.37   6.275%   $54.5935   $54.59   $54.60   $54.60  
  7 purchase totals = $728.04       $800.1918   $800.19   $800.20   $800.10