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 $161.82   13.811%   $184.169   $184.17   $184.15   $184.20  
  Purchase #2 $45.92   13.824%   $52.268   $52.27   $52.25   $52.30  
  Purchase #3 $250.85   12.812%   $282.9889   $282.99   $283.00   $283.00  
  Purchase #4 $76.48   7.354%   $82.1043   $82.10   $82.10   $82.10  
  Purchase #5 $246.32   9.527%   $269.7869   $269.79   $269.80   $269.80  
  Purchase #6 $99.40   4.416%   $103.7895   $103.79   $103.80   $103.80  
  Purchase #7 $175.31   3.595%   $181.6124   $181.61   $181.60   $181.60  
  7 purchase totals = $1,056.10       $1,156.7190   $1,156.72   $1,156.70   $1,156.80