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 $247.41   10.230%   $272.72   $272.72   $272.70   $272.70  
  Purchase #2 $42.31   5.708%   $44.7251   $44.73   $44.75   $44.70  
  Purchase #3 $151.80   12.567%   $170.8767   $170.88   $170.90   $170.90  
  Purchase #4 $166.46   12.535%   $187.3258   $187.33   $187.35   $187.30  
  Purchase #5 $39.57   9.808%   $43.451   $43.45   $43.45   $43.50  
  Purchase #6 $186.34   9.426%   $203.9044   $203.90   $203.90   $203.90  
  Purchase #7 $116.38   6.858%   $124.3613   $124.36   $124.35   $124.40  
  7 purchase totals = $950.27       $1,047.3643   $1,047.37   $1,047.40   $1,047.40