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 $59.84   13.832%   $68.1171   $68.12   $68.10   $68.10  
  Purchase #2 $144.97   8.113%   $156.7314   $156.73   $156.75   $156.70  
  Purchase #3 $12.95   12.420%   $14.5584   $14.56   $14.55   $14.60  
  Purchase #4 $129.37   4.612%   $135.3365   $135.34   $135.35   $135.30  
  Purchase #5 $179.74   5.866%   $190.2835   $190.28   $190.30   $190.30  
  Purchase #6 $103.96   4.205%   $108.3315   $108.33   $108.35   $108.30  
  Purchase #7 $104.31   5.298%   $109.8363   $109.84   $109.85   $109.80  
  7 purchase totals = $735.14       $783.1947   $783.20   $783.25   $783.10