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 $60.37   8.766%   $65.662   $65.66   $65.65   $65.70  
  Purchase #2 $228.48   9.793%   $250.855   $250.86   $250.85   $250.90  
  Purchase #3 $236.31   12.635%   $266.1678   $266.17   $266.15   $266.20  
  Purchase #4 $97.94   13.296%   $110.9621   $110.96   $110.95   $111.00  
  Purchase #5 $140.49   8.797%   $152.8489   $152.85   $152.85   $152.80  
  Purchase #6 $213.30   3.517%   $220.8018   $220.80   $220.80   $220.80  
  Purchase #7 $108.25   13.593%   $122.9644   $122.96   $122.95   $123.00  
  7 purchase totals = $1,085.14       $1,190.2620   $1,190.26   $1,190.20   $1,190.40