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 $206.88   13.572%   $234.9578   $234.96   $234.95   $235.00  
  Purchase #2 $192.42   5.622%   $203.2379   $203.24   $203.25   $203.20  
  Purchase #3 $18.64   6.654%   $19.8803   $19.88   $19.90   $19.90  
  Purchase #4 $226.98   4.663%   $237.5641   $237.56   $237.55   $237.60  
  Purchase #5 $106.42   9.355%   $116.3756   $116.38   $116.40   $116.40  
  Purchase #6 $224.52   9.209%   $245.196   $245.20   $245.20   $245.20  
  Purchase #7 $109.64   5.456%   $115.622   $115.62   $115.60   $115.60  
  7 purchase totals = $1,085.50       $1,172.8337   $1,172.84   $1,172.85   $1,172.90