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 $187.59   10.118%   $206.5704   $206.57   $206.55   $206.60  
  Purchase #2 $236.88   10.623%   $262.0438   $262.04   $262.05   $262.00  
  Purchase #3 $70.44   3.437%   $72.861   $72.86   $72.85   $72.90  
  Purchase #4 $60.84   11.177%   $67.6401   $67.64   $67.65   $67.60  
  Purchase #5 $107.32   3.199%   $110.7532   $110.75   $110.75   $110.80  
  Purchase #6 $212.92   3.848%   $221.1132   $221.11   $221.10   $221.10  
  Purchase #7 $67.30   10.263%   $74.207   $74.21   $74.20   $74.20  
  7 purchase totals = $943.29       $1,015.1887   $1,015.18   $1,015.15   $1,015.20