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 $240.27   11.751%   $268.5041   $268.50   $268.50   $268.50  
  Purchase #2 $122.46   9.697%   $134.3349   $134.33   $134.35   $134.30  
  Purchase #3 $144.59   13.283%   $163.7959   $163.80   $163.80   $163.80  
  Purchase #4 $43.85   12.736%   $49.4347   $49.43   $49.45   $49.40  
  Purchase #5 $128.68   13.830%   $146.4764   $146.48   $146.50   $146.50  
  Purchase #6 $58.56   5.653%   $61.8704   $61.87   $61.85   $61.90  
  Purchase #7 $240.65   13.396%   $272.8875   $272.89   $272.90   $272.90  
  7 purchase totals = $979.06       $1,097.3039   $1,097.30   $1,097.35   $1,097.30