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 $177.43   11.444%   $197.7351   $197.74   $197.75   $197.70  
  Purchase #2 $226.78   5.819%   $239.9763   $239.98   $240.00   $240.00  
  Purchase #3 $20.91   6.608%   $22.2917   $22.29   $22.30   $22.30  
  Purchase #4 $205.45   8.297%   $222.4962   $222.50   $222.50   $222.50  
  Purchase #5 $28.58   8.325%   $30.9593   $30.96   $30.95   $31.00  
  Purchase #6 $87.74   7.130%   $93.9959   $94.00   $94.00   $94.00  
  Purchase #7 $184.40   7.555%   $198.3314   $198.33   $198.35   $198.30  
  7 purchase totals = $931.29       $1,005.7859   $1,005.80   $1,005.85   $1,005.80