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 $169.83   8.392%   $184.0821   $184.08   $184.10   $184.10  
  Purchase #2 $216.56   9.283%   $236.6633   $236.66   $236.65   $236.70  
  Purchase #3 $197.46   6.592%   $210.4766   $210.48   $210.50   $210.50  
  Purchase #4 $177.54   13.645%   $201.7653   $201.77   $201.75   $201.80  
  Purchase #5 $89.59   4.856%   $93.9405   $93.94   $93.95   $93.90  
  Purchase #6 $58.29   13.421%   $66.1131   $66.11   $66.10   $66.10  
  Purchase #7 $122.87   12.622%   $138.3787   $138.38   $138.40   $138.40  
  7 purchase totals = $1,032.14       $1,131.4196   $1,131.42   $1,131.45   $1,131.50