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 $33.59   13.552%   $38.1421   $38.14   $38.15   $38.10  
  Purchase #2 $191.78   6.193%   $203.6569   $203.66   $203.65   $203.70  
  Purchase #3 $244.56   4.836%   $256.3869   $256.39   $256.40   $256.40  
  Purchase #4 $120.61   8.792%   $131.214   $131.21   $131.20   $131.20  
  Purchase #5 $22.66   10.472%   $25.033   $25.03   $25.05   $25.00  
  Purchase #6 $196.70   9.855%   $216.0848   $216.08   $216.10   $216.10  
  Purchase #7 $213.97   12.360%   $240.4167   $240.42   $240.40   $240.40  
  7 purchase totals = $1,023.87       $1,110.9344   $1,110.93   $1,110.95   $1,110.90