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 $212.28   9.802%   $233.0877   $233.09   $233.10   $233.10  
  Purchase #2 $80.61   7.451%   $86.6163   $86.62   $86.60   $86.60  
  Purchase #3 $160.32   8.241%   $173.532   $173.53   $173.55   $173.50  
  Purchase #4 $34.50   3.549%   $35.7244   $35.72   $35.70   $35.70  
  Purchase #5 $101.35   8.646%   $110.1127   $110.11   $110.10   $110.10  
  Purchase #6 $92.67   4.159%   $96.5241   $96.52   $96.50   $96.50  
  Purchase #7 $209.44   10.222%   $230.849   $230.85   $230.85   $230.80  
  7 purchase totals = $891.17       $966.4462   $966.44   $966.40   $966.30