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 $82.69   13.574%   $93.9143   $93.91   $93.90   $93.90  
  Purchase #2 $127.89   10.498%   $141.3159   $141.32   $141.30   $141.30  
  Purchase #3 $205.51   13.269%   $232.7791   $232.78   $232.80   $232.80  
  Purchase #4 $234.68   13.751%   $266.9508   $266.95   $266.95   $267.00  
  Purchase #5 $156.29   4.284%   $162.9855   $162.99   $163.00   $163.00  
  Purchase #6 $165.81   8.490%   $179.8873   $179.89   $179.90   $179.90  
  Purchase #7 $85.66   12.470%   $96.3418   $96.34   $96.35   $96.30  
  7 purchase totals = $1,058.53       $1,174.1747   $1,174.18   $1,174.20   $1,174.20