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 $218.93   5.611%   $231.2142   $231.21   $231.20   $231.20  
  Purchase #2 $63.33   10.454%   $69.9505   $69.95   $69.95   $70.00  
  Purchase #3 $149.62   11.184%   $166.3535   $166.35   $166.35   $166.40  
  Purchase #4 $188.45   5.210%   $198.2682   $198.27   $198.25   $198.30  
  Purchase #5 $199.64   6.626%   $212.8681   $212.87   $212.85   $212.90  
  Purchase #6 $98.59   4.119%   $102.6509   $102.65   $102.65   $102.70  
  Purchase #7 $31.72   4.663%   $33.1991   $33.20   $33.20   $33.20  
  7 purchase totals = $950.28       $1,014.5045   $1,014.50   $1,014.45   $1,014.70