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 $160.98   9.283%   $175.9238   $175.92   $175.90   $175.90  
  Purchase #2 $182.52   11.347%   $203.2305   $203.23   $203.25   $203.20  
  Purchase #3 $166.88   8.239%   $180.6292   $180.63   $180.65   $180.60  
  Purchase #4 $93.34   4.203%   $97.2631   $97.26   $97.25   $97.30  
  Purchase #5 $246.44   9.513%   $269.8838   $269.88   $269.90   $269.90  
  Purchase #6 $223.60   11.278%   $248.8176   $248.82   $248.80   $248.80  
  Purchase #7 $115.43   8.794%   $125.5809   $125.58   $125.60   $125.60  
  7 purchase totals = $1,189.19       $1,301.3289   $1,301.32   $1,301.35   $1,301.30