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 $55.89   8.673%   $60.7373   $60.74   $60.75   $60.70  
  Purchase #2 $53.67   13.508%   $60.9197   $60.92   $60.90   $60.90  
  Purchase #3 $196.52   13.524%   $223.0974   $223.10   $223.10   $223.10  
  Purchase #4 $225.28   9.561%   $246.819   $246.82   $246.80   $246.80  
  Purchase #5 $223.87   10.731%   $247.8935   $247.89   $247.90   $247.90  
  Purchase #6 $124.81   9.530%   $136.7044   $136.70   $136.70   $136.70  
  Purchase #7 $32.73   6.621%   $34.8971   $34.90   $34.90   $34.90  
  7 purchase totals = $912.77       $1,011.0684   $1,011.07   $1,011.05   $1,011.00