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 $80.83   13.433%   $91.6879   $91.69   $91.70   $91.70  
  Purchase #2 $162.75   9.766%   $178.6442   $178.64   $178.65   $178.60  
  Purchase #3 $150.69   9.533%   $165.0553   $165.06   $165.05   $165.10  
  Purchase #4 $88.41   8.378%   $95.817   $95.82   $95.80   $95.80  
  Purchase #5 $24.83   5.122%   $26.1018   $26.10   $26.10   $26.10  
  Purchase #6 $123.39   12.383%   $138.6694   $138.67   $138.65   $138.70  
  Purchase #7 $71.35   7.420%   $76.6442   $76.64   $76.65   $76.60  
  7 purchase totals = $702.25       $772.6198   $772.62   $772.60   $772.60