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 $92.71   10.651%   $102.5845   $102.58   $102.60   $102.60  
  Purchase #2 $38.25   3.644%   $39.6438   $39.64   $39.65   $39.60  
  Purchase #3 $132.56   6.847%   $141.6364   $141.64   $141.65   $141.60  
  Purchase #4 $92.41   10.588%   $102.1944   $102.19   $102.20   $102.20  
  Purchase #5 $91.46   13.285%   $103.6105   $103.61   $103.60   $103.60  
  Purchase #6 $116.93   11.625%   $130.5231   $130.52   $130.50   $130.50  
  Purchase #7 $232.31   12.546%   $261.4556   $261.46   $261.45   $261.50  
  7 purchase totals = $796.63       $881.6483   $881.64   $881.65   $881.60