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 $66.51   4.635%   $69.5927   $69.59   $69.60   $69.60  
  Purchase #2 $234.68   10.843%   $260.1264   $260.13   $260.15   $260.10  
  Purchase #3 $120.82   4.619%   $126.4007   $126.40   $126.40   $126.40  
  Purchase #4 $66.43   7.306%   $71.2834   $71.28   $71.30   $71.30  
  Purchase #5 $169.64   11.416%   $189.0061   $189.01   $189.00   $189.00  
  Purchase #6 $78.51   6.457%   $83.5794   $83.58   $83.60   $83.60  
  Purchase #7 $245.48   5.180%   $258.1959   $258.20   $258.20   $258.20  
  7 purchase totals = $982.07       $1,058.1846   $1,058.19   $1,058.25   $1,058.20