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 $56.51   6.758%   $60.3289   $60.33   $60.35   $60.30  
  Purchase #2 $182.27   11.335%   $202.9303   $202.93   $202.95   $202.90  
  Purchase #3 $41.61   11.335%   $46.3265   $46.33   $46.35   $46.30  
  Purchase #4 $163.87   8.252%   $177.3926   $177.39   $177.40   $177.40  
  Purchase #5 $197.47   3.805%   $204.9837   $204.98   $205.00   $205.00  
  Purchase #6 $207.65   6.444%   $221.031   $221.03   $221.05   $221.00  
  Purchase #7 $105.50   7.127%   $113.019   $113.02   $113.00   $113.00  
  7 purchase totals = $954.88       $1,026.0120   $1,026.01   $1,026.10   $1,025.90