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 $60.33   13.724%   $68.6097   $68.61   $68.60   $68.60  
  Purchase #2 $197.57   9.560%   $216.4577   $216.46   $216.45   $216.50  
  Purchase #3 $200.58   11.588%   $223.8232   $223.82   $223.80   $223.80  
  Purchase #4 $61.78   5.697%   $65.2996   $65.30   $65.30   $65.30  
  Purchase #5 $147.71   5.157%   $155.3274   $155.33   $155.35   $155.30  
  Purchase #6 $197.47   4.622%   $206.5971   $206.60   $206.60   $206.60  
  Purchase #7 $126.42   9.366%   $138.2605   $138.26   $138.25   $138.30  
  7 purchase totals = $991.86       $1,074.3752   $1,074.38   $1,074.35   $1,074.40