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 $53.86   11.586%   $60.1002   $60.10   $60.10   $60.10  
  Purchase #2 $198.84   9.477%   $217.6841   $217.68   $217.70   $217.70  
  Purchase #3 $116.52   3.806%   $120.9548   $120.95   $120.95   $121.00  
  Purchase #4 $241.80   5.477%   $255.0434   $255.04   $255.05   $255.00  
  Purchase #5 $165.64   3.287%   $171.0846   $171.08   $171.10   $171.10  
  Purchase #6 $16.70   12.367%   $18.7653   $18.77   $18.75   $18.80  
  Purchase #7 $231.96   12.105%   $260.0388   $260.04   $260.05   $260.00  
  7 purchase totals = $1,025.32       $1,103.6712   $1,103.66   $1,103.70   $1,103.70