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 $6.29   10.451%   $6.9474   $6.95   $6.95   $6.90  
  Purchase #2 $248.48   13.662%   $282.4273   $282.43   $282.45   $282.40  
  Purchase #3 $202.45   12.773%   $228.3089   $228.31   $228.30   $228.30  
  Purchase #4 $207.57   12.153%   $232.796   $232.80   $232.80   $232.80  
  Purchase #5 $177.35   12.768%   $199.994   $199.99   $200.00   $200.00  
  Purchase #6 $221.41   11.122%   $246.0352   $246.04   $246.05   $246.00  
  Purchase #7 $31.50   13.177%   $35.6508   $35.65   $35.65   $35.70  
  7 purchase totals = $1,095.05       $1,232.1596   $1,232.17   $1,232.20   $1,232.10