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 $216.25   11.773%   $241.7091   $241.71   $241.70   $241.70  
  Purchase #2 $191.57   11.505%   $213.6101   $213.61   $213.60   $213.60  
  Purchase #3 $29.47   7.616%   $31.7144   $31.71   $31.70   $31.70  
  Purchase #4 $11.47   9.616%   $12.573   $12.57   $12.55   $12.60  
  Purchase #5 $221.52   6.844%   $236.6808   $236.68   $236.70   $236.70  
  Purchase #6 $197.95   3.465%   $204.809   $204.81   $204.80   $204.80  
  Purchase #7 $67.89   3.262%   $70.1046   $70.10   $70.10   $70.10  
  7 purchase totals = $936.12       $1,011.2010   $1,011.19   $1,011.15   $1,011.20