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 $83.85   13.849%   $95.4624   $95.46   $95.45   $95.50  
  Purchase #2 $157.97   8.578%   $171.5207   $171.52   $171.50   $171.50  
  Purchase #3 $161.27   10.732%   $178.5775   $178.58   $178.60   $178.60  
  Purchase #4 $66.72   4.212%   $69.5302   $69.53   $69.55   $69.50  
  Purchase #5 $234.67   3.112%   $241.9729   $241.97   $241.95   $242.00  
  Purchase #6 $17.37   11.196%   $19.3147   $19.31   $19.30   $19.30  
  Purchase #7 $103.62   13.234%   $117.3331   $117.33   $117.35   $117.30  
  7 purchase totals = $825.47       $893.7115   $893.70   $893.70   $893.70