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 $46.82   8.387%   $50.7468   $50.75   $50.75   $50.70  
  Purchase #2 $58.97   3.542%   $61.0587   $61.06   $61.05   $61.10  
  Purchase #3 $78.78   11.675%   $87.9776   $87.98   $88.00   $88.00  
  Purchase #4 $130.50   13.145%   $147.6542   $147.65   $147.65   $147.70  
  Purchase #5 $159.37   6.350%   $169.49   $169.49   $169.50   $169.50  
  Purchase #6 $50.30   10.385%   $55.5237   $55.52   $55.50   $55.50  
  Purchase #7 $121.29   7.683%   $130.6087   $130.61   $130.60   $130.60  
  7 purchase totals = $646.03       $703.0597   $703.06   $703.05   $703.10