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 $91.86   3.842%   $95.3893   $95.39   $95.40   $95.40  
  Purchase #2 $61.99   6.133%   $65.7918   $65.79   $65.80   $65.80  
  Purchase #3 $238.99   7.312%   $256.4649   $256.46   $256.45   $256.50  
  Purchase #4 $5.30   13.220%   $6.0007   $6.00   $6.00   $6.00  
  Purchase #5 $50.59   8.369%   $54.8239   $54.82   $54.80   $54.80  
  Purchase #6 $196.41   13.573%   $223.0687   $223.07   $223.05   $223.10  
  Purchase #7 $235.42   8.415%   $255.2306   $255.23   $255.25   $255.20  
  7 purchase totals = $880.56       $956.7699   $956.76   $956.75   $956.80