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 $68.27   13.766%   $77.668   $77.67   $77.65   $77.70  
  Purchase #2 $57.65   5.715%   $60.9447   $60.94   $60.95   $60.90  
  Purchase #3 $102.61   13.132%   $116.0847   $116.08   $116.10   $116.10  
  Purchase #4 $166.60   9.614%   $182.6169   $182.62   $182.60   $182.60  
  Purchase #5 $10.75   5.409%   $11.3315   $11.33   $11.35   $11.30  
  Purchase #6 $200.35   12.670%   $225.7343   $225.73   $225.75   $225.70  
  Purchase #7 $89.65   12.304%   $100.6805   $100.68   $100.70   $100.70  
  7 purchase totals = $695.88       $775.0606   $775.05   $775.10   $775.00