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 $59.41   12.852%   $67.0454   $67.05   $67.05   $67.00  
  Purchase #2 $215.86   9.780%   $236.9711   $236.97   $236.95   $237.00  
  Purchase #3 $241.40   9.175%   $263.5485   $263.55   $263.55   $263.50  
  Purchase #4 $74.65   8.127%   $80.7168   $80.72   $80.70   $80.70  
  Purchase #5 $234.60   7.200%   $251.4912   $251.49   $251.50   $251.50  
  Purchase #6 $22.98   11.614%   $25.6489   $25.65   $25.65   $25.60  
  Purchase #7 $154.89   8.642%   $168.2756   $168.28   $168.30   $168.30  
  7 purchase totals = $1,003.79       $1,093.6975   $1,093.71   $1,093.70   $1,093.60