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 $152.63   11.257%   $169.8116   $169.81   $169.80   $169.80  
  Purchase #2 $186.95   7.704%   $201.3526   $201.35   $201.35   $201.40  
  Purchase #3 $124.85   8.648%   $135.647   $135.65   $135.65   $135.60  
  Purchase #4 $93.51   10.113%   $102.9667   $102.97   $102.95   $103.00  
  Purchase #5 $82.37   3.564%   $85.3057   $85.31   $85.30   $85.30  
  Purchase #6 $60.59   6.403%   $64.4696   $64.47   $64.45   $64.50  
  Purchase #7 $109.31   5.814%   $115.6653   $115.67   $115.65   $115.70  
  7 purchase totals = $810.21       $875.2185   $875.23   $875.15   $875.30