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 $62.85   4.693%   $65.7996   $65.80   $65.80   $65.80  
  Purchase #2 $149.40   7.116%   $160.0313   $160.03   $160.05   $160.00  
  Purchase #3 $243.29   10.109%   $267.8842   $267.88   $267.90   $267.90  
  Purchase #4 $109.61   8.547%   $118.9784   $118.98   $119.00   $119.00  
  Purchase #5 $116.80   6.734%   $124.6653   $124.67   $124.65   $124.70  
  Purchase #6 $143.72   10.670%   $159.0549   $159.05   $159.05   $159.10  
  Purchase #7 $230.82   10.402%   $254.8299   $254.83   $254.85   $254.80  
  7 purchase totals = $1,056.49       $1,151.2436   $1,151.24   $1,151.30   $1,151.30