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 $203.36   11.249%   $226.236   $226.24   $226.25   $226.20  
  Purchase #2 $66.92   3.222%   $69.0762   $69.08   $69.10   $69.10  
  Purchase #3 $113.72   3.259%   $117.4261   $117.43   $117.45   $117.40  
  Purchase #4 $226.39   9.363%   $247.5869   $247.59   $247.60   $247.60  
  Purchase #5 $115.33   5.796%   $122.0145   $122.01   $122.00   $122.00  
  Purchase #6 $149.67   13.217%   $169.4519   $169.45   $169.45   $169.50  
  Purchase #7 $95.57   8.716%   $103.8999   $103.90   $103.90   $103.90  
  7 purchase totals = $970.96       $1,055.6915   $1,055.70   $1,055.75   $1,055.70