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 $61.63   12.574%   $69.3794   $69.38   $69.40   $69.40  
  Purchase #2 $132.57   4.517%   $138.5582   $138.56   $138.55   $138.60  
  Purchase #3 $67.26   9.642%   $73.7452   $73.75   $73.75   $73.70  
  Purchase #4 $49.59   9.613%   $54.3571   $54.36   $54.35   $54.40  
  Purchase #5 $206.32   12.118%   $231.3219   $231.32   $231.30   $231.30  
  Purchase #6 $191.52   4.543%   $200.2208   $200.22   $200.20   $200.20  
  Purchase #7 $183.55   9.661%   $201.2828   $201.28   $201.30   $201.30  
  7 purchase totals = $892.44       $968.8654   $968.87   $968.85   $968.90