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 $126.59   6.116%   $134.3322   $134.33   $134.35   $134.30  
  Purchase #2 $192.83   6.850%   $206.0389   $206.04   $206.05   $206.00  
  Purchase #3 $64.51   4.523%   $67.4278   $67.43   $67.45   $67.40  
  Purchase #4 $25.90   6.264%   $27.5224   $27.52   $27.50   $27.50  
  Purchase #5 $215.95   4.736%   $226.1774   $226.18   $226.20   $226.20  
  Purchase #6 $113.36   8.399%   $122.8811   $122.88   $122.90   $122.90  
  Purchase #7 $112.96   8.868%   $122.9773   $122.98   $123.00   $123.00  
  7 purchase totals = $852.10       $907.3571   $907.36   $907.45   $907.30