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 $54.77   5.447%   $57.7533   $57.75   $57.75   $57.80  
  Purchase #2 $168.45   5.262%   $177.3138   $177.31   $177.30   $177.30  
  Purchase #3 $21.86   12.860%   $24.6712   $24.67   $24.65   $24.70  
  Purchase #4 $86.79   10.320%   $95.7467   $95.75   $95.75   $95.70  
  Purchase #5 $45.32   4.714%   $47.4564   $47.46   $47.45   $47.50  
  Purchase #6 $23.50   3.675%   $24.3636   $24.36   $24.35   $24.40  
  Purchase #7 $74.79   3.344%   $77.291   $77.29   $77.30   $77.30  
  7 purchase totals = $475.48       $504.5960   $504.59   $504.55   $504.70