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 $43.60   6.531%   $46.4475   $46.45   $46.45   $46.40  
  Purchase #2 $181.62   11.558%   $202.6116   $202.61   $202.60   $202.60  
  Purchase #3 $121.60   13.539%   $138.0634   $138.06   $138.05   $138.10  
  Purchase #4 $22.72   9.116%   $24.7912   $24.79   $24.80   $24.80  
  Purchase #5 $196.95   12.855%   $222.2679   $222.27   $222.25   $222.30  
  Purchase #6 $153.42   13.676%   $174.4017   $174.40   $174.40   $174.40  
  Purchase #7 $32.48   6.645%   $34.6383   $34.64   $34.65   $34.60  
  7 purchase totals = $752.39       $843.2216   $843.22   $843.20   $843.20