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 $55.86   3.270%   $57.6866   $57.69   $57.70   $57.70  
  Purchase #2 $84.67   8.613%   $91.9626   $91.96   $91.95   $92.00  
  Purchase #3 $51.35   13.786%   $58.4291   $58.43   $58.45   $58.40  
  Purchase #4 $214.73   8.284%   $232.5182   $232.52   $232.50   $232.50  
  Purchase #5 $233.50   5.214%   $245.6747   $245.67   $245.65   $245.70  
  Purchase #6 $242.27   7.315%   $259.9921   $259.99   $260.00   $260.00  
  Purchase #7 $173.70   7.373%   $186.5069   $186.51   $186.50   $186.50  
  7 purchase totals = $1,056.08       $1,132.7702   $1,132.77   $1,132.75   $1,132.80