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 $96.51   10.481%   $106.6252   $106.63   $106.65   $106.60  
  Purchase #2 $178.30   4.606%   $186.5125   $186.51   $186.50   $186.50  
  Purchase #3 $27.66   4.160%   $28.8107   $28.81   $28.80   $28.80  
  Purchase #4 $60.57   12.431%   $68.0995   $68.10   $68.10   $68.10  
  Purchase #5 $236.50   4.423%   $246.9604   $246.96   $246.95   $247.00  
  Purchase #6 $164.75   11.391%   $183.5167   $183.52   $183.50   $183.50  
  Purchase #7 $211.74   6.355%   $225.1961   $225.20   $225.20   $225.20  
  7 purchase totals = $976.03       $1,045.7211   $1,045.73   $1,045.70   $1,045.70