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 $248.77   11.371%   $277.0576   $277.06   $277.05   $277.10  
  Purchase #2 $212.65   10.521%   $235.0229   $235.02   $235.00   $235.00  
  Purchase #3 $27.48   11.553%   $30.6548   $30.65   $30.65   $30.70  
  Purchase #4 $64.29   5.791%   $68.013   $68.01   $68.00   $68.00  
  Purchase #5 $68.63   7.185%   $73.5611   $73.56   $73.55   $73.60  
  Purchase #6 $237.80   4.406%   $248.2775   $248.28   $248.30   $248.30  
  Purchase #7 $104.25   12.771%   $117.5638   $117.56   $117.55   $117.60  
  7 purchase totals = $963.87       $1,050.1507   $1,050.14   $1,050.10   $1,050.30