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 $66.60   5.107%   $70.0013   $70.00   $70.00   $70.00  
  Purchase #2 $109.36   10.616%   $120.9697   $120.97   $120.95   $121.00  
  Purchase #3 $163.74   5.488%   $172.7261   $172.73   $172.75   $172.70  
  Purchase #4 $191.69   7.518%   $206.1013   $206.10   $206.10   $206.10  
  Purchase #5 $51.54   7.820%   $55.5704   $55.57   $55.55   $55.60  
  Purchase #6 $245.73   12.801%   $277.1859   $277.19   $277.20   $277.20  
  Purchase #7 $220.70   4.629%   $230.9162   $230.92   $230.90   $230.90  
  7 purchase totals = $1,049.36       $1,133.4709   $1,133.48   $1,133.45   $1,133.50