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 $145.52   10.815%   $161.258   $161.26   $161.25   $161.30  
  Purchase #2 $217.80   9.268%   $237.9857   $237.99   $238.00   $238.00  
  Purchase #3 $210.27   11.836%   $235.1576   $235.16   $235.15   $235.20  
  Purchase #4 $5.58   6.159%   $5.9237   $5.92   $5.90   $5.90  
  Purchase #5 $205.80   5.635%   $217.3968   $217.40   $217.40   $217.40  
  Purchase #6 $127.50   12.342%   $143.2361   $143.24   $143.25   $143.20  
  Purchase #7 $11.54   13.135%   $13.0558   $13.06   $13.05   $13.10  
  7 purchase totals = $924.01       $1,014.0137   $1,014.03   $1,014.00   $1,014.10