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 $203.65   11.819%   $227.7194   $227.72   $227.70   $227.70  
  Purchase #2 $248.56   5.602%   $262.4843   $262.48   $262.50   $262.50  
  Purchase #3 $169.33   7.496%   $182.023   $182.02   $182.00   $182.00  
  Purchase #4 $41.89   6.596%   $44.6531   $44.65   $44.65   $44.70  
  Purchase #5 $52.47   10.773%   $58.1226   $58.12   $58.10   $58.10  
  Purchase #6 $180.28   13.226%   $204.1238   $204.12   $204.10   $204.10  
  Purchase #7 $51.66   13.415%   $58.5902   $58.59   $58.60   $58.60  
  7 purchase totals = $947.84       $1,037.7164   $1,037.70   $1,037.65   $1,037.70