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 $176.26   4.424%   $184.0577   $184.06   $184.05   $184.10  
  Purchase #2 $239.72   12.653%   $270.0518   $270.05   $270.05   $270.10  
  Purchase #3 $141.66   9.168%   $154.6474   $154.65   $154.65   $154.60  
  Purchase #4 $220.89   7.602%   $237.6821   $237.68   $237.70   $237.70  
  Purchase #5 $108.64   10.279%   $119.8071   $119.81   $119.80   $119.80  
  Purchase #6 $66.61   13.319%   $75.4818   $75.48   $75.50   $75.50  
  Purchase #7 $5.40   10.729%   $5.9794   $5.98   $6.00   $6.00  
  7 purchase totals = $959.18       $1,047.7073   $1,047.71   $1,047.75   $1,047.80