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 $58.33   8.372%   $63.2134   $63.21   $63.20   $63.20  
  Purchase #2 $108.55   11.779%   $121.3361   $121.34   $121.35   $121.30  
  Purchase #3 $160.29   3.249%   $165.4978   $165.50   $165.50   $165.50  
  Purchase #4 $239.52   3.737%   $248.4709   $248.47   $248.45   $248.50  
  Purchase #5 $89.57   8.538%   $97.2175   $97.22   $97.20   $97.20  
  Purchase #6 $61.56   10.659%   $68.1217   $68.12   $68.10   $68.10  
  Purchase #7 $229.87   4.577%   $240.3911   $240.39   $240.40   $240.40  
  7 purchase totals = $947.69       $1,004.2485   $1,004.25   $1,004.20   $1,004.20