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 $49.58   6.824%   $52.9633   $52.96   $52.95   $53.00  
  Purchase #2 $148.38   8.187%   $160.5279   $160.53   $160.55   $160.50  
  Purchase #3 $136.29   10.696%   $150.8676   $150.87   $150.85   $150.90  
  Purchase #4 $203.88   8.195%   $220.588   $220.59   $220.60   $220.60  
  Purchase #5 $50.58   7.674%   $54.4615   $54.46   $54.45   $54.50  
  Purchase #6 $223.66   6.714%   $238.6765   $238.68   $238.70   $238.70  
  Purchase #7 $5.81   5.714%   $6.142   $6.14   $6.15   $6.10  
  7 purchase totals = $818.18       $884.2268   $884.23   $884.25   $884.30