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 $89.34   8.164%   $96.6337   $96.63   $96.65   $96.60  
  Purchase #2 $211.89   11.589%   $236.4459   $236.45   $236.45   $236.40  
  Purchase #3 $231.49   6.248%   $245.9535   $245.95   $245.95   $246.00  
  Purchase #4 $164.42   4.556%   $171.911   $171.91   $171.90   $171.90  
  Purchase #5 $55.97   9.129%   $61.0795   $61.08   $61.10   $61.10  
  Purchase #6 $6.91   12.568%   $7.7784   $7.78   $7.80   $7.80  
  Purchase #7 $201.72   8.367%   $218.5979   $218.60   $218.60   $218.60  
  7 purchase totals = $961.74       $1,038.3999   $1,038.40   $1,038.45   $1,038.40