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 $153.27   5.623%   $161.8884   $161.89   $161.90   $161.90  
  Purchase #2 $80.36   9.516%   $88.0071   $88.01   $88.00   $88.00  
  Purchase #3 $209.81   5.229%   $220.781   $220.78   $220.80   $220.80  
  Purchase #4 $205.83   5.792%   $217.7517   $217.75   $217.75   $217.80  
  Purchase #5 $230.85   7.187%   $247.4412   $247.44   $247.45   $247.40  
  Purchase #6 $53.92   3.551%   $55.8347   $55.83   $55.85   $55.80  
  Purchase #7 $32.95   4.841%   $34.5451   $34.55   $34.55   $34.50  
  7 purchase totals = $966.99       $1,026.2492   $1,026.25   $1,026.30   $1,026.20