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 $246.70   6.506%   $262.7503   $262.75   $262.75   $262.80  
  Purchase #2 $181.31   11.479%   $202.1226   $202.12   $202.10   $202.10  
  Purchase #3 $155.84   11.261%   $173.3891   $173.39   $173.40   $173.40  
  Purchase #4 $14.81   6.182%   $15.7256   $15.73   $15.75   $15.70  
  Purchase #5 $160.45   3.283%   $165.7176   $165.72   $165.70   $165.70  
  Purchase #6 $210.51   10.658%   $232.9462   $232.95   $232.95   $232.90  
  Purchase #7 $102.36   3.807%   $106.2568   $106.26   $106.25   $106.30  
  7 purchase totals = $1,071.98       $1,158.9082   $1,158.92   $1,158.90   $1,158.90