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 $126.34   6.834%   $134.9741   $134.97   $134.95   $135.00  
  Purchase #2 $214.83   10.706%   $237.8297   $237.83   $237.85   $237.80  
  Purchase #3 $65.58   4.814%   $68.737   $68.74   $68.75   $68.70  
  Purchase #4 $46.80   13.233%   $52.993   $52.99   $53.00   $53.00  
  Purchase #5 $178.34   12.689%   $200.9696   $200.97   $200.95   $201.00  
  Purchase #6 $227.32   7.123%   $243.512   $243.51   $243.50   $243.50  
  Purchase #7 $34.73   3.682%   $36.0088   $36.01   $36.00   $36.00  
  7 purchase totals = $893.94       $975.0242   $975.02   $975.00   $975.00